You have finally made it far enough in your career that someone has slid into your DMs asking for a meetup to "pick your brain." Congrats! This is an honor, even if you do wish to charge for your consulting services (hey, your time is valuable!). Personally, I try to help out non-vulturey young people wishing to break into the biz for free (then again, I rarely check my DMs). 

In any case, this particular sort of social interaction calls for a unique approach to venue-picking. On the surface, it is casual, but it realistically needs to be kept professional, which is why a coffee shop is so often the go-to. But, I don't know about you, I just can't have my brain picked without a little lubrication, so I prefer grabbing a big girl drink with my potential mentee. This option requires a whole new set of criteria. The bar needs to be cool (so that this person thinks I am cool), but not trashy, and not too date night-y. Appropriate for after-work cocktails and pricey enough that you'll both want to put a cap on the night after no more than two rounds of cocktails and chatter. 

It's a delicate business (before you even get to the business part) but don't overthink it - because I've gone ahead and overthought it for you.