I doubt any doc would worry about language as long as he's saying a word or two. It's (supposedly) very normal for boys to talk later & not say much until age 2 or so. But you can bring it up if you're concerned (particularly if you suspect another issue like a hearing problem or poor comprehension).
Anyway...
My doc really doesn't ask us much. He assumes everything is fine & normal and we tell him if there's anything we're particularly worried about. We went to his 18mo appt (he hadn't been in 6mos) and all he did was weigh him & check his head circumference. I gave him an estimate for his height and he asked if there were any problems & we went on our way. But the doc knows us pretty well (I was in there a lot a few months ago for my own medical issues) and he's seen DS at all my appointments so I think his informal observations were enough to know he's fine. I honestly wish we'd just skipped the 18mo appt too, it just wasn't worth our time & we know he's on track/ahead physically, developmentally, etc.
But as far as what to ask her... think of it like an interview. What would you like to know about this doc? Do you want someone who will be knowledgeable with extended breastfeeding, for example, and able to provide advice on that? Do you want her to be up-to-date on any specific medical issues that run in the family? Do you want her to be familiar with alternative medicine? Do you just want her to be able to check for ear infections and strep throat? It really all depends what you're looking for in a doc.
I think our first appointment, I told the doc (who's also a homeopath & family doc) about our family, our choices (vegan, no vax, avoid mainstream medicine, ext. BF, family bed, etc.) and just discussed these things with him. It was really easy to gauge where he stood on most of those issues -- though I already knew from other MDC mamas that he was largely supportive of most of them anyway. I love that we can be totally open with our doc & he will look at our whole family picture. I don't have to hide that DS sleeps poorly or is incredibly high-needs, and I know he won't over-react or tell us to do things that go against our instincts & beliefs. To me this was sooo important in a doctor, because I have had A LOT of trouble with doctors in the past.
But if you just want someone who can prescribe occasional antibiotics when necessary or something, then you might not need to know much besides, "What will you do if he has an ear infection" etc. I know some people don't want to discuss anything with the doc except true medical issue (like that rash)... and if the doc is very mainstream, yeah you probably want to avoid discussing sleep. Also if you have any questions about the practice as a whole -- scheduling appointments, what number to call in an emergency, how soon can she see a sick kid... then you can ask those as well -- or arrive a little early and ask the receptionist or nurse (if she has either, mine doesn't!!).