BDF, CFI, EJO, GNU, ?

The first letter of each term are the letters in the prime numbered positions according to alphabetical order. So, the first letter is K.

The difference between second letter of each term has no pattern.(3, 4, 4)

So, let's check with the link between first and second letters.

BDF => B+2 = D

CFI => C+3 = F

EJO => E+5 = J

GNU => G+7 = N

So, it is addition of prime numbers.

 K+11 = V

Similarly, checking for third letter and second letter.

BDF => D+2 = F

CFI => F+3 = I

EJO => J+5 = O

GNU => N+7 = U

In the same way V+11 = G

KVG is the answer.