Hi, I use Kinefx to retarget animations, and my animation source need to apply an euler filter first.
But I can't find any tutorial about how to apply euler filter to fbx animation import node.

I'm not sure Euler Filter would help with anything post import, since the rotation on the joints in KineFX are not represented by euler angles, but by a matrix and most likely interpolated through slerp

so any potential Euler values from FBX may be already lost, which on one hand can automatically solve most of the cases where Euler Filter used to be necessary, but on the other hand can introduce new issues if Euler angles between keys were larger than 180° in which case you may get inverted rotation or lose revolutions

the actual issue however depends on your particular animation of course