DL has no Sky Clubs in Europe. You get same-day access to Skyteam partner operated lounges (but not third party operated lounges) on departure on international flights according to DL rules. There are no Skyteam partner operated lounges in FRA, CPH, or ARN, but when flying AF/KL, you will often get an invitation to the third party lounges.

https://www.delta.com/skyclub/viewSk...Request.action