Get the object id when button is added to the detail schema

Hi,

I added a button next to (+) button on a detail. The code is added to the detail schema, and the button is always enabled. I want to get the ID of the "parent" object, the object where the detail is in.

I tried this.Get("Id") but I get unknown (I think it's because it's looking for the Id of the detail and there is no active row

Can you please help me get the Id?

(When pressing the 'Select all schools' btn I want to get the PD event Id)

https://i.imgur.com/7ftN8E3.png

Thanks,

Chani