It means, "I don't know where [I, presumably] would be without her." It could just as easily be, "... you/he/ she/it would be without her." Without a context, it's impossible to say for cetain.
'Donde Estudias?' means 'Where do you study?'
I think you mean Donde which is Where (in english)
¿dónde estás? means where are you?
hola donde estas
el=he ella=she
Donde = when The other words are not (or don't look) Spanish
'Donde estas ahora' = Where are you now
"Where does it stay?"
It means "where do you pay?"
Where were you (familiar) born?
where are you from
Y donde queda eso means "and where is that located" !