12, 34, 10, 11, 12, 5, 6 ,7, 13, 14, ?, ?
Logically, what two numbers should replace the question marks?

15 and 11

1 + 2 + 3 + 4 = 10, then insert next two numbers 11, 12 and add digits 1 + 1 + 1 + 2 = 5. Insert next two numbers 6, 7 and add digits 6 + 7 = 13. Insert next two numbers 14, 15 and add digits 1 + 4 + 1 + 5 = 11.