How to Add a V-Cut Line in Fritzing?

Without knowing the purpose for ‘your’ v-cut, I can only assume you want to section the board.

One way to do that is this post. Note, I’ve updated/posted several posts on making a PCB ‘Board’ with cutouts. Line-cuts are just as simple to do.

Consider this info:
• PCB’s have different thicknesses, thus, cutting through and not-cutting through… i.e., the Depth of C-cut.
• If paneling is the goal (for snapping off smaller pcb’s) a normal cut is all you need.
• Identifying what the Vendor should do is recommended - add Notes to the Request For Quote (RFQ).
• Some manufacturers use Laser to cut - thus, no V-Cut. The Kerf is a clean cut.
• Some manufacturers use CNC/Mill to cut - they can define “Holding Tag’s”. Again, add Notes to RFQ (Holding Tags usually have a shallower height (versus the board thickness) to make snapping-off easier.