IMHO, OpenCL knowledge is not required to program in Aparapi. But then aparapi has very limited functionality, and it may not be possible to write any algorithm in APARAPI. Also you will find a lot of things very strange if you jump into it without any prior experience in GPGPU.
So I would suggest you to go through some introductory material on OpenCL, so you can then understand how aparapi acts as a wrapper. And then you can understand for, what algorithms aparapi would be good enough.