If your WC has a monitoring software you can check on it. if not, you should plug the pump on your CPU_FAN header on your motherboard, then you can check in your bios monitoring page the CPU_FAN rpm, that, in this case, will indicate the water pump RPM, if its 0 then its dead.
you can try on a SYS_FAN header as well on your motherboard if you have one free for testing purposes.
I can see its a corsair WC, then it has the corsair link software or iCUE that will tell your pump RPM, same deal, if its 0 its either not powered or dead.