A lot will depend on how you want the hole to end , for a flat end I did this and Iassumed your hole angle of 25degrees is not the same angle as the slope.
Create a plane at 25degrees to the vertical

create 2nd plane where you want the hole to end parallel to the one you just created

To make it easier placing the circle create an axis where the two planes cross

Draw circle on 2nd plane using axis to locate

Cut extrude to beyond the outside of your cone. I have made the part transparent so you can see extent of hole

If you don't mind how the hole ends then just create the first plane and draw the circle on that and cut to vertical plane

result

Edited By JasonB on 11/01/2019 08:26:49