Use Point/On,A,Atangl with the arc reference and the angle in degrees. The angle must be within the arc sweep.
Full Answer
Use Point/On,A,Atangl. Specify the arc reference and the angle in degrees. The angle must fall within the arc sweep — between the start and end angles of the arc.
XyzPilot Example
A0 = Arc: centre(0,0), r=50, start=0, end=90 CCW
Point/On, A0, Atangl, 45, 0
→ P0 = (35.355, 35.355) [at 45 degrees — within sweep]
Point/On, A0, Atangl, 90, 0
→ P1 = (0, 50) [at 90 degrees — arc end point]
Point/On, A0, Atangl, 120, 0
→ Error: 120 degrees is outside the arc sweep (0 to 90)