2 solidworks will pick the rip edges for you by process of elimination.
Convert cylinder to sheet metal solidworks.
If you cannot insert an axis then the model is not an exact cylinder and cannot be unfolded.
Here is your sheet metal box.
If you can insert an axis the model is an exact cylinder.
As a test try to insert an axis on the cylindrical face.
When dealing with sheet metal parts a best practice is to define it as a sheet metal part sooner rather than later.
Notice the three features added.
However sheet metal parts created with the lofted bends feature avoid this limitation and unfold appropriately.