We do not have enough data on this route to provide a reliable graph showing how many days before departure it is the best to book.
However, usually the closer it is to the departure, the more expensive the tickets are.
The most popular airlines on the route Copenhagen - Valencia: Ryanair (FR), Iberia (IB), TAP (TP).
The cheapest flights you can book on the route Kastrup (CPH) - Manises (VLC).
There is no direct flight on the route from Copenhagen to Valencia
The shortest flights with change last about 18h 30min.