The first sentence does not specify who 'her' refers to. It could be Johnsy, but it could also be someone else.
The second sentence does not mention who is asked. Maybe he asked Johnsy, or maybe someone else.
The two sentences will be the same if
1.He wanted to know from Johnsy what had happened to Johnsy.
2.He wanted to know (from Johnsy) what had happened to Johnsy.
But they will be different if in the first sentence he asked Johnsy about someone else:
1.He wanted to know from Johnsy what had happened to Ella.
and in the second he asked someone else about Johnsy:
2.He wanted to know from us what had happened to Johnsy.
If we do not specify who gets asked, or if a pronoun is used, it is assumed that we already have that information. Without the context, it is hard to say whether the two sentences mean the same or not.