Did scientists find ebola's reservoir? If not, what kind of species can it be? Are there any theories?

Fruit bats are thought to have been the source.

 

Watch what you eat.

I read about some bats that had been tested positive (for either virus' RNA or antibodies) but didn't develop any symptoms. Is there an explanation for that?

Even if present, viruses to not cause the same pathologies in all hosts. In fact there are many examples in which viruses that have co-evolved with their hosts cause few or no symptoms. Eventually they may get integrated into the genome and just get propagated with the host.

I think it has not been firmly established that fruit bats are the sources, but they are considered a very likely candidate.