Open the model on 0xr.space, press More, then Info: the panel lists AUTHOR, LICENSE and SOURCE. They are read from the file. A GLB from Sketchfab carries its author, licence and source inside it, and a license.txt in Sketchfab's format beside the model, as in its ZIP downloads, is read too; when both are there, license.txt wins. A gallery model's page under 0xr.space/m has a Licence and attribution section that states the credit in one sentence.
When the file says nothing, AUTHOR shows Unknown, LICENSE shows N/A and SOURCE shows Local import. That does not mean the model is free to use, only that the credit was not in the file. These fields cannot be edited in Model Explorer. A share link carries the author and licence with the model, so the person you send it to sees them too.
The creator's name, the title, the licence name with a link to it, a link to the source where there is one, and a note if you changed the model. For example: Old Chair by Jane Doe, licensed under CC BY 4.0, from sketchfab.com, scaled and recoloured.
The file carries no author. OBJ, STL and most other formats have nowhere to put one, so look on the page you downloaded it from.
Yes. Every gallery card shows the creator and licence, and models with a limited licence are not offered.
No. CC0 asks for none, though giving one is still courteous.