On the player's side:
DATAs from the same hime are considered 1 attack.
Multi-hitting nukes are considered 1 attack. i.e. Susanoo, Svarog etc
Multi-Element nukes are considered multiple attacks. i.e. Meido Amon.
Skills with multiple activation are considered multiple attacks. But those aren't available yet on taco. i.e. Ra, Arianrhod etc
On the enemy's side:
Most multi-hitting random nukes are considered 1 attack.
The only few exceptions I can think of is Dysnomia's 4-hit trigger special attack.
The best way to differentiate them is to see if it can kill a covering unit with defiance buff (survive lethal attack with 1 hp 1 time). Dysnomia's attack can proc the buff with the first killing hit, and then kill the defending unit with the next.