First, NGC6946 is one of the finest galaxies in the northern sky and a BIG favorite of mine. I encourage you to keep trying.
You have plenty of aperture. How are your conditions? A dark sky is extremely helpful for these ~low surface brightness face-on galaxies. Though mV8.8 sounds like a bright object, the large size of NGC6946 yields surface brightness m13.8 and that is a better indicator of what difficulty one may have finding it and how it may appear in the eyepiece. Have you tried observing NGC6939, the open cluster @ 40' NW just across the border in Cepheus and placed in a very similar star field, similarly obscured by Milky Way dust? It is like-sized and slightly brighter with slightly higher surface brightness. It's a good starting point. Sometimes they can look surprisingly similar. As for most galaxies, you want to look first for the brighter core of NGC6946 and then you can start to piece together the halo that can be resolved into arms and can show quite bright H-II regions. From a dark site, experienced observers report easily seeing via 13" Dobs the eastern arm and its forked nature as well as the bright H-II region SW of the core. I 1st saw this one via unmodified XT10i from the club's SE Oklahoma dark site. The importance of dark sky conditions is paramount. It is completely invisible from my white zone home site.
Once you find this one, the fun begins. NGC6946 is an object that can reward more experimentation than many galaxies. Try higher mag to see if more detail presents. Try a filter (I use narrowband O-III here) to see if H-II regions present, perhaps in places you did not notice them w/o filter. And it's only a matter of who's alive and looking to see the next in a long series of supernovae this baby produces that gave it its name.
Good luck with your observations.
Edited by havasman, 28 June 2020 - 07:33 PM.