That's a clearomizer CE2 or CE3 (non-rebuildable), gently unscrew the tip, if you have juice in it decide if it's worth saving or not, if you want to save gently drip back in your juice bottle, if not, run the clearomizer under as hot a water as you can stand out of your sink. flip it over blow from bottom to empty the tank...repeat rinse and blowing out 4-10x until the wicks are nice and clear
Once done, blow from the top where the tip was to clear out the air vent tube
fill your tank, put 1 to 2 drips in center hole, put back on tip, hold over paper towel, and blow thru the clearomizer (you might get a tiny bit of juice out the bottom hole, this primes your wick
Put back on battery and puff puff puff