Can I use this power supply DC output terminals to create a dual power supply?
Can I make a +24V -24V dual power supply by tying B and C together and making this joint as GND

No, that is NOT possible.

This is a 1 x 24 DC supply. If it was 2 x 24 V then the connectors would be placed more separate to emphasize that they're independent. It would be indicated on the device as well as: 2 x 24 V

I think terminals A and B are shorted already and so are C and D.

Get your multimeter out, switch off this supply, disconnect it from mains and put the multimeter in continuity mode or resistance mode. Now measure it. I give you 99.99% change that A=B and C=D.