U	P	D	W
T	O	B	M
P	N	F	O
Q	N	C	?

What is the letter for the missing letter and why ?

Don't know.... see only 3 vowels, O twice... wondering if missing letter is U, but no time now to study it. The only reason is use that tact is that there are 2 Ns together in a column, which threw me off, and there is a vowel in every row...

But I' guessing U, quickly.

U	P	D	W
T	O	B	M
P	N	F	O
Q	N	C	?

What is the letter that should replace the question mark ?

1-J
2-K
3-L
4-M
5-N

Got your message. Have friends visiting from out of town. Not going to work on it, sorry.