Hi @Manusz
as I wrote in this other thread, I am also very new to digikam and there is still a lot for me to explore. So please excuse me if I am missing something.
To my knowledge, there is no function that (automatically) links externally created JPGs to the corresponding RAWs.
At the moment I am testing the grouping function to link my Jpgs to the original RAWs. It works quite well for my needs. I also like the fact that you can assign keywords for all group members at the same time. However, the grouping process has to be started manually, but that is not a problem for me.
Cheers, Roland