You can copy either one assignment or all assignments from one course to another. You should have "teacher" role in both courses to perform this operation.
Select "Assignments" in the top bar -
Then select "Import Assignment" from the bottom of the list of assignments -
Select "Course" and then should present a list of all the courses where you have the teacher role -
Select the course and then select "Select assignment" which should present you with a list of assignments in that course and also an option "All assignments" at the bottom -
Selecting "All assignments" will copy all the assignments of one class into another.