A PC requires skill check to know details about a spell or creature. Know(arcana) for details on dragons and for details on spells. Spellcraft is about casting spells, identifying magic items, crafting magic items, and identifying spells as they are being cast. Your GM could allow either and may adjust the DC around +/- 5.
AoN Umbral Dragon, Adult CR14
It has 3 Special Attacks Breath Weapon(Su) (50-ft. cone, DC 23, 12d8 negative energy, DC 23), Crush(Ex), Shadow Breath(Su) Three times per day, an adult or older umbral dragon can breathe a cone of shadows. Creatures who fail a Fortitude save are blinded for 1d4 rounds and take 1 point of Str drain per age category possessed by the dragon (6 Str). A successful save negates the blindness and reduces Str drain to 1d4 points (Fort 23 Con based). Notice there's no frequency limitation on Shadow Breath other than 3/d.
The description in the dragon's entry leaves it open for your GM to consider as is it undead shadows or planar shadow based (as it is from the Shadow Plane). The strength damage seems to be similar to shadow(undead) CR3 where Strength Damage (Su) A shadow’s touch deals 1d6 points of Strength damage to a living creature. This is a negative energy effect. A creature dies if this Strength damage equals or exceeds its actual Strength score. My caution is "cone of shadows" is not a "cone of undead shadows" and with these things if it is not explicit it is not a match. Secondly an Ability Drain is far worse than Ability Damage. The blindness seems more darkness(planar shadow) related. Creatures with the blind condition are not likely to survive an encounter with an adult dragon. From a Rules Forum perspective "not a match" means No, not a negative energy effect as it doesn't say so.
Death ward:N4 The subject is immune to energy drain and any negative energy effects, including channeled negative energy.
