a general search while in game? ie. searching for where to buy bags???
You can’t “search” per se, the implication there being that you can be quite granular in your parameters. You can ask a guard where to find some NPCs though, such as the Auction House (where you can buy bags from other players) or where your class trainers are. These are around capital cities and usually have the word “guard” as a part of their name.
For other things, such as where you can find a vendor that sells bag, google is probably your best bet here. I think some addons will do this but it’s easy enough to type a search into google. For example, if I’m playing Era and I want to buy a bag and I’m in Ironforge, I can search for wow classic era ironforge bag vendor. The first couple hits give me an NPC called Pithwick, who sells bags between 6 and 12 slots for increasingly higher prices.
That’s not in-game and so while that may not have been the answer you were looking for, I hope it helps. Good luck!