OP,
A larger context photo of the wall would help?
To find the DPC you need to use, say, a flat bladed screwdriver to to start scraping out a little mortar from the beds. Start at ground level and work up bed by bed.
Any DPC would probably be a slate DPC although other materials were used.
Your air brick is very low - maybe the ground level has been raised over the years?
Presumably, you have a suspended floor - your joist tails might be at risk of rotting?
Is there damp damage showing on the inside of the solid wall?