How to identify the wall type and studs for drilling

I need to anchor an Ikea bookcase and a drawer to the wall, but despite days of Internet research I am not able to identify where I can drill a hole in my wall. I have tried knocking on the wall to listen to the ‘depth’ of the sound to distinguish masonry from drywall. I think the wall onto which I am planning anchor the furniture is a drywall based on the hollow sound upon knocking. Now I am trying to identify the studs within the wall, but the sound method is not helping as every knock sounds the same. I bought a stud finder to no avail as it is not giving me reproducible results and it’s not identify studs in a periodic pattern which makes me think that there is something wrong with it (or the way I use it). I found the hole in the picture. I am wondering if it is possible to identify the wall type from the picture of this hole (whether it is masonry or drywall).

I’d be very grateful if someone can guide me on how to identify where I can drill a hole in the wall to attach somewhat heavy furniture like a wardrobe or a bookcase.

Thanks in advance!