I'm not 100% sure of what type of feature you are trying to add, but it looks like you want a mesh opening for air intake.
Your Szkic1 is no good. You'll want to repair it, or delete 99% of it as I have. There are a bunch of extra lines and arcs in it which prevent it from being useful. There are also hundreds of lines in it, and that is rather slow and difficult to work with.
Make it smaller, experiment to see what works, then make it more complex if you need to.
After repairing, or deleting most of the sketch lines, reorder the feature tree so Szkic1 is at the bottom.
Extrude Szkic1 as a surface extrude. The end distance does not matter, just make it go through the part.
Use Trim Surface to do a mutual trim. Here I selected all of the surfaces, then just the one main surface I want to keep.
Hide or delete the remaining bodies that are no longer needed. You'll see the grill pattern has started to appear.
To finish off the design, I'd suggest using some type of pattern to put the remaining cuts into the surface, but I don't think your surface model is symmetrical, or perfectly aligned with the reference planes.
I think a really good thing to try is the Fill Pattern option, but you'll need to first split your main surface to have the area for the grill defined.