You can browse them, and create new ones, by
1) Creating a new mod (new project tab) of the type "Add-on"
2) Don't create a new level (well, you can, but it's not necessary)
3) Open the Stats editor (third-last icon on the top bar, one that looks like a vertical bar graph)
4) Under Projects -> Shared click on the disclosure triangle next to "ItemCombos"
5) Click on ItemCombos
If you also wish to see the recipes specific to the DOS2 main campaign, you can add a dependency of your mod on Origins (Project menu -> Project Settings... -> Dependecy tab) and then browse the ItemCombos of Origins in the Stats editor.