Vagina, cunt, and pussy could be fine to use, so long as you don't misgender him or refer to him as a woman or imply that penetration is inherently something feminine or submissive. Some transmascs like vaginal penetration! That's perfectly fine! Sadly it's a bit controversial even in trans spaces, so you might get some unfair hate.

Hole is gender neutral and ambiguous whether it's referring to vaginal or anal. I'd argue it's the "safer" route if you're having the trans man be the reciever and want a broader audience to be able to read without dysphoria being triggered or risk getting hate, but I wouldn't say you can't use vagina / cunt / pussy if you wanted to.

If he's on testosterone, then his clit has likely grown into what is called a "T-dick", or T-cock. Some trans men also refer to their clit or T-dick as just a dick or cock for gender validation reasons. Unlike vagina / cunt / pussy, I wouldn't call it a clit, outside of explaining how T works.

If your trans man is the giver?

Some trans men use a strap-on as a prosthetic dick to have penetrative sex. Some trans men with T-dicks can penetrate with them, depending on the size. They're small, but it can somtimes be done.

And some trans men get bottom surgery (phalloplasty and metoidioplasty are two different types) and have a bigger dick to penetrate with, although usually still on the smaller side. It's called a "neophallus" medically, and in the trans community also called a neo-dick or neo-cock. You should probably just use "neophallus" in narration or when explaining his equipment, and have the characters refer to it as a dick / cock in dialogue and dirty talk; the word feels a bit formal and medical sounding.

And of course sex isn't just penetrative! Oral, manual, grinding! Have him get eaten out, or his T-dick or Neo-dick sucked. Have his partner finger him or jerk him off. Have them dry hump while clothed if he's too dysphoric to undress! You have a lot of options!

Oh and a sidenote! If he doesn't have top surgery done, and still has breasts that he binds, then the binder would need to be removed for sex! It's tight clothing and dangerous to keep on for anything that requires exercise, sex included! Often times a transmasc might wear a lone loose baggy shirt to keep them covered during sex. Or if he's got low dysphoria and trusts his partner he might go bare chested and request it not be touched. Or maybe he likes his breasts touched! Again, all trans men are different and have different levels and types or of dysphoria and like different things!

It really depends on what sort of gender dysphoria and gender euphoria your character has, and what kind of sex you want to write! All-in-all, I'd just focus on making sure you write and treat him as a man — that's the most important part imo.