In Haydn's F minor variations for piano, how does one attack the continuous trills, one note after the other?
I'm going to assume you mean this part of Hob.XVII:6. This is from the Edition Peters score.
I think that the extension of the trill notation throughout the whole bar is simply a convenience to avoid having to write tr~~~tr~~~tr~~~tr~~~; it should be played simply as a succession of trills. Although what's going on with the fingering in bar 86, I have no idea.