If one Key Result is needing to be used in multiple OKRs, you can simply clone the Key Result and select "Sync progress and notes".
Steps to clone and sync Key Results
1. Navigate to the Key Result, and from the dropdown menu, select "Clone KR".
2. In the pop-up select the option to "Keep the current progress for the cloned KR". If you choose to "Reset the progress for the cloned KR" you won't be able to sync its progress and update notes with the cloned KRs.
3. Select whether to send notifications to the owner(s) of the KR being cloned
4. Check "Keep progress and updates in sync" if you would like the updates to any of the cloned KR's to be synced to all of them.
5. Lastly, choose where to clone the KR.