Can you copy a commander spell with Strionic Resonator to get it twice?

Strionic Resonator's ability reads: '{2}, {T}: Copy target triggered ability you control.' A triggered ability is an ability that begins with 'when,' 'whenever,' or 'at.' Casting your commander is casting a spell, not a triggered ability, so Strionic Resonator simply cannot target it. (CR 603.1, 706.10)

To copy a spell on the stack, you need effects that specifically say they copy a spell, such as Twincast or Dual Casting. Those interact with spells on the stack under CR 706.10 and 706.11, which govern copying objects.

Strionic Resonator can interact with your commander indirectly — for example, if your commander has an 'enters the battlefield' triggered ability, the Resonator could copy that triggered ability once the commander has resolved and entered the battlefield. That would give you a second instance of the triggered effect, but you would still only have one copy of the commander itself. (CR 603.1)

Concrete example: You cast Kaalia of the Vast. Kaalia resolves and triggers 'Whenever Kaalia of the Vast attacks, you may put an artifact, creature, or enchantment card from your hand onto the battlefield.' You activate Strionic Resonator targeting that triggered ability — you get a second trigger, putting two permanents into play. But you never got a second copy of Kaalia as a spell on the stack.

In short: Strionic Resonator copies triggered abilities (CR 603.1), not spells (CR 112.1). You cannot use it to get your commander spell twice.