I wanted to know what skin lightener works for dark african american skin, I heard Hydroquinone 6% lightens dark skin, how can I get that? And will it work on my skin type? Or is there any lightener that someone has used that they can refer me to?

You could try MEDICATED SEKKISEI, especially its cosmetic lotion, but never try its emulsion. It is quite popular now in China and has top reputation.

Why not first try a 4% hq for a while along with tretinoin to see how your skin reacts?