I want to draw windows on the fusulage but cant seem to get the sketch button to work. File is attached
You've not include the part files with this assembly.
To answer your question, 2d sketch needs a planar surface/face, etc. whereas your surface is not not planner. So either try 3d sketch OR Make a plane and create your sketch on that plane. Finally project that sketch onto this face (using either of split, wrap, project curve, etc commands)
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