How can I make a table for the arm of the sofa?

I would suggest either a sofa tray or a C table, examples below.

https://visualhunt.com/sofa-tray-table

Here is a video showing how to use slats and webbing to diy a basic sofa tray. https://www.youtube.com/watch?v=_iz-CzoZ-5Y

Glue or Staple Fabric or Yarn or Twine or Leather Strips to a Board that is Wide enough for your Stuff, after that glue dries, you want to Straddle that board with some dowels, so you gotta glue or staple the Whatever you get to the Dowels too.

It is very easy to do. Just don't overdo the glue snd remember the dowels are not what holds this sofa arm table in place, the Whatever Material you get, will hold it in place. The dowels are only to make it look pretty rather than look like you just Duct Taped a Board to the Arm of the Sofa. I mean that ain't the look you're going for, I'm sure. If you want it to cling rather than hang loose, use rubber or velcro strips.

Hello. This is a nice project to consider. I have seen folding ones in the thrift store but this DIY construction would be more attractive and structural. Hope this video helps.

DIY Sofa Arm Table

https://youtu.be/LeAphpvHfJg

we built this sofa cup holder for beer but it would work for wine too ;) https://www.charlestoncrafted.com/couch-arm-cup-holder/