I don't have an ethernet adapter for my MacBook Pro, and after reinstalling from the recovery partition and wiping the drive, I get a flashing 'file folder' icon with a questionmark. Can I somehow establish the wifi connection in order to boot?

Hey aenlic, thank you for posting here in Apple Support Communities.

We understand that you're receiving a flashing question mark folder after an wiping your Mac computer's hard drive, and we'd be happy to help you with that. To start, can you tell us if you've already performed the first few sets of troubleshooting steps shown here: If your Mac starts up to a question mark

If so, reinstalling the macOS software will be our next step and you should definitely be able to connect your Mac computer to a Wi-Fi network. For more information, please check out the "Connect to the internet using Wi-Fi" section of the following resource: Use macOS Recovery on an Intel-based Mac

Please be sure to use a secure, known-good Wi-Fi network and not a VPN, Personal Hotspot or public Wi-Fi network.

Let us know if that helps.

Cheers!