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If you just want the reference in that position. Set up a new plane that will intersect exaction where you need it. Then you can either use a sketch reference - toggle it's type to make it a line within the sketch.
Or you can make a curve in place using Curve from surface Intersection within the Wireframe environment.
Or you could insert a curve on the surface between the to adjacent lines.
Lot of options - depends on what you want to achieve and how much the underlying geometry is expected to change - and then update the new part.