Q:

either + singular + 'have' or 'has'?

Is it legal to use has in the following question?

Would you tell me please whether either my friend Joey or me has to visit the manager tomorrow?

Or, instead, should I use have rather than has?

A:

I think that 'either' here is being used in the sense that it is Joey, or 'me' (not both). So, the proper conjugation of the verb to have would be has.
You would generally use plural when you have 'either of', for example:

Would you tell me please whether either of us have to visit the manager tomorrow?

