Which two letters of alphabet always comes together in spell?
Q is a tricky alphabet.
Scrabble
players are acutely aware that Q is a tricky letter. To use a Q in the game, a
player must also find an available U The fact that Q is the second most rarely
used letter in the alphabet certainly doesn’t make using Q any easier.

How do Q and U work together?
In English, QU is always used as a pair of letters representing a single speech sound for the sound /kw/ (a voiceless labiovelar stop). 'Q's pairing with U is a Latin invention that has its origin in Greek. The letter Koppa, which Q is based on, would appear before a rounded vowel where otherwise a sound like /k/ or /g/ would be used. But, a few other letters, like C, also designated the same sound but in different letter combinations. As C gradually came to represent more and more of these instances, Q became primarily dependent on U to express any sound at all. This is quite a quibble for a full-fledged member of the Latin (now English) alphabet.Q without U is used to represent sounds not often found in English but typical in Semitic languages. Loan words such as Qur’an and Iraq are examples of Q’s guttural /k/ sound.
NOTE:-
QWERTY
But when we heard the word "Qwerty" then it's different. Reason being. QWERTY is not the English word because if you read about Qwerty this will comes from KEYBOARD look into your keyboard there keys start with Q-W-E-R-T-Y and also if your trying to translalate it there has no result of it. thats why U directly not following the Q in QWERTY spell. here I have a few more words those not belong to any english word nither any meaning as well. like:- Qatar, Qiana, Qi, qabala, qawwali.