Is it wrong to orgasm inside my wife first before giving her cunnilingus. I would like to ask her to let me?

Is it wrong? Of course not! I'd hazard to guess that you don't think it's wrong for your wife to swallow when she gives you a blow job, right? So, if it's OK for her to get your semen in her mouth, why would it be wrong for you to get your own cum in your mouth?

The only possible problem here is if your wife isn't comfortable with the idea. Since I don't know her, I really can't say much to that question. Were I in your position, I'd probably just go ahead and go down on her after sex sometime, but the fact that you'd feel like you needed to ask does suggest that at least one of you is/might be uncomfortable about the idea, in which case it's always best to ask. (And I wish you the best of luck getting the answer you want!)