Do I need to apply for a visa or is a 144 hour visa enough?

Hi,
i'm traveling to Seoul from Amsterdam next month. My flight to Seoul is this: Amsterdam - Guangzhou - Seoul. I know that a 144-hour twov applies in this case but I need some help with my flight back. My flight back to Amsterdam is: Seoul- Guangzhou - Beijing - Amsterdam. I don't know if a 144-hour visa applies in this case. So do I need to apply for a normal visa or is a 144-hour twov enough?
Thank you in advance!