Encoder spec isn't as determinate as decoder. More specifically, when input=0000, what output gets is left to the designer and unless you clarify it, no one can answer your question.
I don't know what 'V' you are referring to is and there is no such thing as a priority in a simple encoder.
A 4-2 encoder has only 2 bit outputs which can tell which one of 4bits is on, but having 8bit inputs, none of the 4bits could be '1' which makes the possible input patterns 5. Apparently, 2 bit outputs isn't enough.
Again, unless you make your encoder spec clear, no asnwer can be given.