When I move with Rek'Sai Swarm Queen to an unoccupied battlefield do I get the attack trigger?

No, you do not get the attack trigger when moving Rek'Sai, Swarm Queen to an unoccupied battlefield.

According to the established rules and the FAQ regarding Rek'Sai, Swarm Queen:

1. Open Showdown: When you move Rek'Sai to an empty battlefield, you initiate an "open showdown." At this stage, there is no combat, and no units have the "Attacker" or "Defender" designation.
2. Trigger Condition: Rek'Sai's ability ("When I attack...") is an Attack Trigger. According to Rule 376.4.d, these triggers only occur when a unit gains the Attacker designation during a combat showdown.
3. Result: Because moving to an empty battlefield does not initiate combat, Rek'Sai does not gain the "Attacker" designation, and therefore her ability does not trigger.

If an opponent later moves a unit into that same battlefield, the open showdown ends and a combat showdown begins. At that moment, Rek'Sai gains the "Attacker" designation, and her ability will trigger then.