Verified answer

there is none. The dieresis (two little dots over the u) is only used after the g, and when is preceeded by a soft vowel (e,i) For example pinguino, verguenza,etc (with the diresis over the u). Which is why no Spanish word can start with u (with dierisis) because it needs to be preceeded by a "g"

No.

EDIT:

Apparently I'm the only one here that knew that was a letter :/ but no, there isn't one. I believe that it is found only after g's. Other than those two, the only other one that comes to mind is bilingüe.

Live long and prosper.

That is not a Spanish letter.

vaca (cow) vacaciones (vacations / holiday) vehiculo (car) there are many others, how many did you need

i do believe that is a german letter ?

U Mad?