In reply to dave_59:
Hi Dave, thanks you for reply.
I had to add some modules with assertions for some muxes in my tb, and in the same files I added the covergouprs for the inputs and outputs of these muxes. There is another module with assertions, outside of my testbench and I want to add covergroups. Signals that are used from this module are instantiated in my top tb file, but I am searching which is the best way to add covergroups for these signals