Stand exactly where you throw the Eye of Ender. Press F3 to open the debug screen. Look directly at the floating Eye of Ender while it is mid-air. Find the XYZ line for your current coordinates, and the Facing line for the angle. The first number after 'Facing/' is your exact Yaw value.

This tool uses triangulation. A single throw creates a straight line pointing towards the Stronghold. A second throw from a completely different location creates another line. The point where these two lines intersect reveals the precise coordinates of the End Fortress.

For high accuracy, change your position by walking roughly 150 to 300 blocks away from your first throw location, preferably perpendicular to the initial flight path. Throwing twice from almost the same spot can cause calculation errors due to nearly parallel lines.