I think that the best way is to find out for your self.
You should be able to figure out which one is the volume knob easy enough.
Check the others and see what they do.
Have everything centered and get a feel for what your low notes and high notes sound like. Then, one at a time, try the extreme settings of each knob and see what effect they have on your low notes and high notes.
When you find that one that brings out your highs more, makes you sound 'thinner', actually makes you high notes sound louder - that's your high EQ
Kind of the same thing for your low and mid EQ.
Check for a p/up blend too. I can't imagine a bass with two separate pick ups that doesn't let you control the blend. Some might mistake it for a low EQ as when you blend toward the P pick up, you'll get a lower deeper sound, and as you blend toward the bridge p/up you'll get a thinner more trebly sound. A blend knob will have a detent - only the volume knob wouldn't.
So when you're checking things out by putting your knobs in the extreme positions, you might be able to tap on the pick ups and see if you are getting sound from one and not the other in one position - and then the opposite in the other extreme setting. If so, that would be a blend knob.
I don't mean for this to sound the wrong way - but I think it's best if you played with your bass and these four knobs until you figure out what each one is. You should be able to tell what each one does.