If you control Strionic Resonator, can you copy a triggered ability from an opponent's permanent?

Strionic Resonator's activated ability reads: '{2}, {T}: Copy target triggered ability you don't control... wait—actually, it copies any triggered ability on the stack. The card text says "Copy target triggered ability. You may choose new targets for the copy." It places no restriction on whose permanent generated the trigger.

Under CR 112.7, an activated ability that copies a spell or ability puts a copy of that ability on the stack. Strionic Resonator targets a triggered ability on the stack (CR 603.1 covers triggered abilities going on the stack), and nothing in its text limits the copy to abilities from your own permanents. You simply need to pay {2} and tap Strionic Resonator while the triggered ability is on the stack.

The copy is created on the stack and is controlled by you, the player who activated Strionic Resonator (CR 706.10). You may also choose new targets for the copy if it has any targets.

Concrete example: Your opponent controls Ob Nixilis, the Fallen and attacks, triggering its landfall-style triggered ability when they played a land. That triggered ability goes on the stack. You activate Strionic Resonator, targeting that triggered ability. A copy is placed on the stack under your control—you benefit from the effect of Ob Nixilis's trigger even though you don't control Ob Nixilis.

Note that you must activate Strionic Resonator while the triggered ability is still on the stack (CR 509.2 covers priority and when players may activate abilities). Once the trigger resolves, it is gone and can no longer be targeted.