So someone on reddit asked about what sex is like for trans women, for the sake of writing a comic. The question was respectful enough, unlike the exploitative shit such questions usually entail. But as is usually the case when cisgender people ask us about our lives, I get the feeling that the very phrasing of the question misses the point. Trans people are people too. I wrote a rather long series of replies trying to unpack why I felt the question missed its target, and I thought it'd be worth repeating here.
 Hey. I'm writing a comic. There is a trans woman in it. She dates and has sex with a cisgendered woman.
I'm not going to get super explicit in the comic, but I don't want the scenes with them to seem disingenuous, so if I may ask some practical questions…
Transwomen who are attracted to women, what do you do exactly? Do you like to have penetrative vaginal sex with them? Do you like to receive oral? Do you prefer that your penis not be verbally acknowledged? Most importantly for my purposes, what kind of language do you like your partner to use when referring to you and your body?
I've known and spoken to trans* people a lot and talked with them about their lives and emotions and all but I would feel kind of weird asking them "So hey, how do you like to fuck? I'm only asking because I want to plagiarize your words and profit off of them financially". It's pretty easy to find writing and essays online by trans* people about what their childhoods where like and how it feels to be them but less in the way of nuts and bolts descriptions of sex. I realize the answers to these questions are likely not the same for everyone, but any perspective you could give me on this would be helpful.
 Well, trans folks are raised in the same prudish culture as cis folks are, so it's no wonder we tend not to talk about sex ;)
Actually, sex is even more complicated for us —as a group, not necessarily as individuals— because of how many trans people (particularly trans women of color) are involved in sex work as a result of the systemic injustice we face. Working in the sex trade, especially when forced to do so to survive, is going to have profound ramifications on how one responds to sex. Most of us here and elsewhere online are middle-class, and therefore cannot speak directly to all the issues this entails.
Transgender people also have to deal with sexual abuse and domestic violence, same as cisgender folks. It's tempting to say we're worse off here than the cisgender population, but it's hard to back that up due to the usual problems of underreporting as well as the interaction with transphobic violence— which often comes as the result of sexual encounters or has a component of sexualized violence incorporated into the hate crime itself.
In general, I'd say that sex is for us much like it is for everyone else. And that includes sex workers, sexual abuse survivors, domestic violence victims, etc, etc. So without knowing more about your character, it's difficult to see what sort of answers you're looking for. The only trans-specific sexual questions I can think of are mechanical details (which are irrelevant if you're not being explicit), choice of terminology (which is personal/individual/unique), or if she's still dealing with extreme issues of dysphoria (in which case I think you want to know more about dysphoria than about sex per se).
 Another thing to bear in mind is that how sex goes is going to have a lot to do with the cis woman too!
Were the two of them together pre-transition? If so, how does she feel about that? How has she dealt with the change in viewing her partner, from seeing her as a man to seeing her as a woman? If the trans woman hasn't had SRS, does the cis woman have hangups about what she's "supposed" to do with "boy parts"? If she's lesbian, she may have issues with identity, past abuse, being actively turned off, etc. If she's bi, she may have issues keeping her interest in men, and what she likes to do with them, segregated from her interest in women and what to do with them. If they were together pre-transition, maybe she's straight but still in love with partner despite that; maybe her straight identity is in crisis, or maybe she's fine with the incongruity.
Remember, it takes two to tango.
 P.S., I hope I don't come off as being too critical. There's just a lot of stuff to unpack here. As a writer, I think the proper way to look at things is that transgenderism is just another character trait— like age, ethnicity, class, or being a veteran, addict, immigrant, etc. Transgenderism isn't something the character does, what she does is work, go to school, fight crime, raise kids, whatever. However, because she is trans, the world is going to look at her and respond to her differently; it's going to throw different obstacles in her way, things that cisgender people don't have to deal with or would react to differently. And all of this applies to sex just as much as to the rest of life.
 Just to throw some personal data in here:
[Trigger Warning: childhood sexual abuse]
I was sexually abused as a child. Consequently I have issues with people going down on me. As an adult I had a couple girlfriends who really enjoy doing that. Because they were so into it, and I was so into them, I didn't want to deny them that pleasure. I spent years with both of them working through these issues: talking about everything, taking it slow, stopping on a dime when need be, tackling the ensuing emotional turmoil. Years of hard work. I eventually got to the point where it no longer immediately squicks me, no longer makes me feel like a worthless disgusting subhuman monster, no longer causes flashbacks, no longer makes me throw my partners out of bed in my sleep, no longer makes me terrified of why she's with me, of what she wants from me, no longer makes me conspire ways to get out, to get away, to run run run,...
Years and years of work to get to the point where I can think to myself, "yeah, I guess I can see why people might like it." Sometimes it can even be pleasurable. But it's never something that could get me off.
And all of this in spite of the fact that I love going down on both men and women, and have never had the slightest issue with doing so. And all of this not having the slightest thing to do with being trans. The only way transgender would come into play here is that maybe, just maybe, I could actually enjoy it once I get SRS and the mechanics of everything changes. I'm curious, definitely willing to give it a shot, but who knows how it'll turn out.
Considering that, in the US, 1 in 5 girls and 1 in 20 boys are victims of childhood sexual abuse, and 1 in 6 women and 1 in 33 men are victims of rape, there's a very good chance that one or both of your characters would have similar issues around sex. It may not be something you want to explore in the comic, but it's definitely something to bear in mind.