I can't find any information for the Mini 2 for placing a drone label. Ofcourse you can place it anywhere you want. But for other drones DJI has created a guide (https://content.djiservice.org/activation/germany-fireproof.html) explaining what's the best place to mount the label. But does someone know where this place is for the Mini 2?

The location is country rule specific.   Here in the UK you can place it anywhere you dont need tools to access. And the font needs to be 3mm tall or better.   I label mine under the battery, but you should check your countries rules.