I read the tooltip but I still don't understand how Shop Player works? I click a player, then click "shop player" and then hover over it again to see who is interested? Is that what it does?

I did that, I got a list of teams that are interested in Anthony Davis, but when I ask them for an offer I get "no offer at this time". Is there no connection between who is interested and who will give an offer? Thx!

(FYI the only players I get offered for AD are Trae and Luka)

You are doing it correctly - what you are seeing is a list of teams who are INTERESTED in that particular player but not necessarily are ABLE to trade for him. In your example with Davis - thats 38m in salary to trade for so for many teams that may be difficult to come up with a package that a) is salary legal and b) not a ridiculous offer to you. You might be willing to take like one 1st and then nothing but scrub salary back but if the AI doesn't think its a reasonable offer to make then it will not make it so while that team may not present an offer to you at least you know they have interest in the player and you can see if there is something you can work out rather than just guessing on every team to see if they want your player.