If someone pointing a shotgun to your head and tell you to learn them all, do it with this steps:
Java2D
Slick2D
LibGDX
LWJGL
Personally, I think that it depends on the starting point you choose and the aim you want to reach. Moreover, I did the opposite movement with different APIs, I started by OpenGL in C, I switched to the competitor of LWJGL and now I use 3D engines most of the time. Being close to the metal was not my aim but a good understanding of low level aspects has helped me to use high level APIs.