UnityGame/Library/PackageCache/com.unity.mathematics/Documentation~/quaternion-multiplication.md

Quaternion multiplication

To rotate a quaternion, use the AxisAngle method. You need to specify the axis of rotation and the angle of rotation, in that order. All are in radians rather than degrees. math.mul multiplies the quaternion, just as with matrices and vectors.

// Unity Mathematics example
void QuaternionMultiplicationUnityMathematics()
{
   var axis = new float3(0.0f, 1.0f, 0.0f);
   var q = quaternion.AxisAngle(axis,math.radians(45.0f));
   var orientation = quaternion.Euler(
       math.radians(45.0f),
       math.radians(90.0f),
       math.radians(180.0f));
   var result = math.mul(q, orientation);
}