I use this when the visual of a letter isn't sticking in the student's head.
Circle the first N together, in the instructions, and that will work as a reference. The child can circle the rest on their own. For a bonus bit of fun you can allow the child to use a different color for each N they find.
For a MESSY DAY activity a finger paint thumb print can work to mark Ns, or even a stamp of the student's choosing. Go nuts!
NOTE: When it comes down to it W, Z, N, V, and M can look like just a bunch of nonsensical zigzags when first learning the name of each letter. It's normal to need to spend some extra time getting a student acquainted with these.