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