What are the question marks on the map mean?

[Sinophile]

I walk up to them, but nothing happens, what am I supposed to do?

[Diamond Encrusted Toaster]

This is an old post but to answer for anyone else confused, the question marks mean to search the area, like you might need to interact with someone in the area or an object.

[Valden21]

It's exactly what the above post said. You're supposed to talk to the different NPCs in the area, and one of the dialogue choices will be to ask them if they know anything about your objective.

[M3ta4]

I cant believe this is a question...