User blog comment:Numinous J/Dir'Rak, Paragon of Entropy/@comment-7709681-20170503221038/@comment-26378838-20170504065522

Thanks for thinking of possible complications with the passive, but considering the new system in the midseason patch where a trail is shown whenever a champion lands an ability on an opposing champion, I think that indicates that the system both recognizes when an ability lands or not and if it lands on a champion or not.

Considering your examples:
 * Pass-through skillshots won't trigger Dir'Rak's passive if they hit a champion, no matter how many minions jumped in front of it beforehand;
 * Even if the target is invulnerable, the hit still registers, prompting a "INVULNERABLE" pop up, so you can still gage whether the skillshot hits an ally or not;
 * Untargetable allies will cause skillshots to miss if these don't hit an ally beyond them;
 * Perhaps I'm forgetting something, but I'm not aware of a skillshot that misses due to or  helicopter hands thingy.
 * If a skillshot hits but does nothing (for example, being consumed by a spell shield), it'll still register the hit, thus not triggering the passive.