Of course you can ask that. You may or may not get the sort of answer you're looking for. (Most of the time, asking my T those kinds of questions, the answer is going to sound like it's coming from a cross between a Zen master and Yoda. That can be frustrating, but it can also be instructive.)
Words matter. When forming the question, I'd say to begin by looking for what it is you actually want to know. You might also consider your reasons for asking the question.
If I asked my T "what's wrong with me?" I'd guess his response is going to steer the conversation in the direction of an inquiry into what i mean by "wrong with me". That's likely to get messy, although there's probably useful stuff to be explored and gained. If I just want to know what he's come up with for a diagnosis, that's exactly what I'd ask. I already know that it's his personal point of view that a "diagnosis" is mostly something that matters to insurance companies. In his version of reality, everyone is different, all traits exist on a continuum, the only meaningful diagnosis HE sees for me is "Scout". There are some things I'm good at. Some things that are challenges, and the goal is to help me find a path to being the best possible version of Scout.
Therapists are individuals too. The response you get will be in keeping with that. Worth asking, if you want to know. I think, for therapy to work well, you should ideally feel free to ask anything.
Well, I asked. Like mentioned above I expected a very long winding response ending in what do you think is wrong?
She surprised me and gave me a very detailed and direct answer, much appreciated. So basically her answer is I am suffering from PTSD and severe disassociation. The cause is what was surprising, absolutely tied in part and started by my CSA but that it was actually additional traumas over the next 7-8 years that finalized and cemented my PTSD. She also commented that I hold myself to impossible standards and refuse to forgive myself for any perceived fault or failure.