How many courses is my party wall?

I’m about to embark on a loft conversion for my ~1960’s bungalow. This will be a full width dormer.

After doing to reading and research, I’m pretty sure I’ll need some steel work. The steel would need to rest on my side of a party wall.

However, my party wall is pretty thin and I’m not entirely sure if it is a single skin or double skin. Is there any easy way I can check this?