To copy a sketch you already must have a sketch so I created one.Now I am gonna close this sketch.
1. Now I am going to select the sketch on the feature tree at the left and I will press Right Ctrl+C, you need to hold Ctrl and then press C.
Now I have made a plane as a reference and moved it a little bit to make it more clear, you do not need to create one, you can copy sketch to whatever plane you want.
I am going to start a sketch on this plane, and then I will just press ight Ctrl+V, hen the sketch should appear.
As you can see the same sketch was copied to a different plane, it is an easy way to save your time, if you want the same sketch on parallel planes you can use Convert Entities.