Term for someone asking "For a friend"

Is there a word that describes the phenomenon, often seen on SE sites, where someone says they are asking a question "for a friend", but actually mean themselves?

I use prosopopoeia, defined at MERRIAM WEBSTER as

a figure of speech in which an imaginary or absent person is represented as speaking or acting

One expression which encapsulates the phenomenon to which you refer is under the guise, M-W defines it as: by saying or acting as if something is other than what it really is

Under [or in] the guise of a helpful friend, the OP is really asking the question for his own benefit.

On call-in talk shows on the radio, for example, a caller might preface his or her comments to the psychologist or psychiatrist by saying,

"A friend of mine is struggling with an addiction problem, and I'm calling to get some advice as to how I can help my friend get free from the downward spiral."

You know what they say:

Denial isn't just a river in Egypt.

As an armchair psychologist, however, I commend the person who calls about his "friend's" addiction. Despite their pretense, at least they realize there's a problem in their own life and are seeking help, albeit indirectly.

As for an OP who asks a question supposedly for a friend, I see nothing particularly wrong with that, unless the OP's motive is to deceive or otherwise hurt another person. Sometimes we just find it hard to admit being ignorant, whether the reluctance stems from pride and/or fear of what others (including peers) might think us, or from some other relatively harmless but perfectly understandable motive.

Another expression which comes to mind is feigned ignorance. One interesting aspect of feigned ignorance is that it can proceed from an ironic perspective. Socrates had mastered the art of feigning ignorance in order to encourage his interlocutor to talk himself into a corner, so to speak. Once that happens, the person who feigned ignorance can then pounce on his prey and eviscerate him verbally, exposing the interlocutor's true ignorance.