There seems to be very little information about the tranny fluid for the 1976 Datsun B210. The clutch is taking too long to disengage, so I wanted to check all of the fluids. However, the words "transmission fluid" only appear in the automatic transmission section, and don't specify which container has the transmission fluid. I'm assuming that it's the one in the picture below, as it has a direct line to the transmission, but the liquid inside it was clear, not red like most transmission fluid. Any help?

I have never owned a Datsun with a hydraulic clutch (like yours). But yes you circled the right container. Your Datsun doesnt have an automatic transmission, it uses normal gearbox oil in the gearbox. Then the clutch hydraulic system don't use what you know as "transmission fluid". The stuff it uses is like brake fluid, as its hydraulic. So it would be clear. Just ask a mechanic to change the fluid in your clutch master cylinder. Then see if that fixes the clutch.

changing the clutch master cylinder fluid will not help. Especially if it is clear (old fluid turns very dark). Yes, per the owners manual it uses DOT 3 brake fluid. There is such a thing as "bleeding the clutch cylinder" but that only needs to be done after replacing the cylinder and never again

Instead, adjust the clutch