Solved
About perpendicular projection (sketch)
Q3:XZ plane is my sketch plane, How to get the“perpendicular projection point” G of point K ? I can't do that by the snap tool or project tool. (the "S" shape curve is drawn in the ZY sketch plane )

Q3:XZ plane is my sketch plane, How to get the“perpendicular projection point” G of point K ? I can't do that by the snap tool or project tool. (the "S" shape curve is drawn in the ZY sketch plane )

When sketching on the XZ plane, use the select references tool

and add the endpoint of your curve that is on the YZ plane. The projection of this point will appear at location "g" as a reference point:

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