No, you are getting completely muddled now!
You connect the optocoupler anode to 3.3 V. The cathode through your 240 Ohm resistor to the ESP output. There is no need to make it an open-collector output. It's just fine! 
Where you do have a problem, is that the optocoupler has an open-drain output. That means you require a pull-up to drive the SK6812 and this limits the response speed. It is not really the correct device but it should work OK with a reasonably low pull-up value and short wiring to the SK6812.