Yet the nominative form is found quite frequently to divide the work of the objective use; for example,—
My son is going to be married to I don't know who.—Goldsmith.
Who have we here?—Id.
Who should I meet the other day but my old friend.—Steele.
He hath given away half his fortune to the Lord knows who.—Kingsley.
Who have we got here?—Smollett.
Who should we find there but Eustache?—Marrvat.
Who the devil is he talking to?—Sheridan.
Exception 2, but he, etc.
406. It is a well-established usage to put the nominative form, as well as the objective, after the preposition but (sometimes save); as,—