So i'm kind of new in car audio and i was wondering if i have a  2 4 ohm HDS212 and i wire them down to 1 ohm would a Q1-750 be enough power or should i go bigger? 

Do you have 1 total dual 4 ohm voice coil driver? Or 2 of them? Kind of hard to understand the way way you wrote the question.

Those sub's I believe are rated for up to 600 RMS each, if you do have 2 of them, giving the pair 750 watts to split between the 2, gives them 375 watts each. Plenty enough to get them moving, but will not maximize their abilities. You would be better looking for an amp in the 1000 - 1500 watt range, in this case.

SQ does offer a 1200 watt monoblock as well.

You have no idea if that is enough power without knowing what alignment they will be in.  Additionally, the power handling rating has absolutely nothing to do with a required power to get to full output, at all.  Period.