To add to this: if your friend arrives in T2B, and assuming it’s on something other than a domestic flight, there is now a transit security point in the remote terminal - until about November 2017 he or she would have had to come to T2A anyway.

Where you decide to meet may depend on what lounge access you both have. The better lounges are generally in T2B (particularly UA), but there’s really not much else there - so if you can both get in a lounge, I’d meet in B, but if you can’t then there’s many more places to sit and have a coffee and something to eat in A.

Allow about 15 minutes walking time each way between the two - if it’s busy with full travelators then you’ll need close to this. The travelators only run from A to B, so if going in the opposite direction there’s no assisted walking and to a certain extent you’ll be going against the flow of traffic (although off the travelators there’s normally plenty of room).