On your current PC:
Settings > Update & Security > Activation
If you have your Microsoft account linked, it should says "Activation: Windows is activated with a digital license linked to your Microsoft account".
On the new PC:
If you're not reinstalling Windows: check in the same place, if it still says this
If you are reinstalling Windows: during the install it will ask for your Microsoft account, will ask if you changed hardware and then you can check in that same menu again