Realistically, if you mean bandwidth, then you'd have to ask Openreach but I suspect they might not tell you for commercial reasons. On the other hand if you means ports then often you can get a good idea by just looking at the physical size of the cabinet and the area it serves.
The number of lines/circuits/ports the dslam may handle.
Mine has four card slots, and a 128 line frame bolted to the side.
I cannot see any frames in the main bit, the extra frame bit was bolted on after the main installation, so I am guessing it may be 128 + 128 with 4 * 64 port cards?
It is a huwei dslam