The Eldritch Invocation Ghostly Gaze allows the Warlock to see through solid objects out to 30' for as long as she concentrates (up to 1 minute).
For our scenario, our Warlock's nemesis has managed to evade the adventurers the warlock travels with by slipping into a panic room. The panic room is behind a 5' thick stone wall, and is 10' x 10', making the entire room within the 30' range of Ghostly Gaze while the Warlock is adjacent to the outer wall (or anywhere within 15' of it).
Weapon attacks are not possible as they cannot penetrate the wall, and many spells are also blocked by the wall as they involve a tangible effect traveling from the Warlock to the target (rays and such).
According to this question about targeting with line of sight but no line of effect, no spells should work. However, it seems certain that Sacred Flame would work as it specifically ignores cover. Is this correct?
Do the circumstances of the Ghostly Gaze spell allow any other spells to work (like Toll the Dead, that does not specify an effect traveling from the caster to the target, but simply "pointing to a target you can see within range")? I'm guessing that the answer is no, since the intent seems to be that there is always a requirement for an unobstructed path to the target unless stated otherwise (such as in Sacred Flame).
So, is Sacred Flame valid to attack the target? Are there any other cantrips that might work? Spells?