Does GTX 285 support dx11?

Even though it supports DirectX 11, the feature level is only 10_0, which can be problematic with many DirectX 11 & DirectX 12 titles.

What was the most powerful GPU in 2013?

1. NVIDIA Geforce GTX 780 Ti.

Is 2GB video card enough for gaming?

2gb is still enough to play any game on the market, you just have to set the settings accordingly (or let geforce experience do it for you).