What's the next value 4 D 7 G 10 J 13

D comes at 4th place ... similarly G and J come at 7 and 10th place respectively ... so at 13th place comes M

Next value would be M, then 16, then P, then 19, then S, then 22, then U, then 25, and finally Y. This is an arithmetic sequence where the difference is + 3, but after the number, the sequence add in the corresponding alphabet in terms of order. For example D is the 4th letter in the alphabet, so it comes after 4.