over 4 years ago - Avanya - Direct link
The save keeps track of this and has a "Subscribe All" button you can use to grab all mods and assets that you had subscribed while playing that save. It does grab things you might have removed, so if you switched a mod or removed some assets you didn't use, those will still be subscribed. So if you do this, it's a good idea to have a look through things and remove anything you don't want.

https://steamcommunity.com/sharedfiles/filedetails/?id=2023107131

Alternately you can use the output log (player.log on Mac and Linux) to find the mods used. To do this you just load the save (which might not work since you're missing mods). Then you open the log and find a list of numbers. This is the Steam IDs for the mods used in the save. You then open a browser and add the ID number to the end of this url: https://steamcommunity.com/sharedfiles/filedetails/?id=
That will take you to the mod's page.

The list looks something like this in the log
The following mods were used when this asset was created: UnlimitedMoney UnlimitedOilAndOre UnlockAll UltimateEyecandy 558661484 597981885 553501635 445589127 515489008 767233815 791221322 608517757