Some details missing here--
1) Are they flying? (Probably required, doubt you'll get a boarding pass equivalent for a guest only)
2) Are you flying? (You don't need to be, you can ask for a pass to get through TSA to visit the SkyClub even if you're not flying).
If you're a DL SkyClub member, and present with your guest, you can bring anyone you want into the SkyClub.