The 1930 census shows Frederick immigrated in 1917 and he first married at age 29. The 1920 census lists Frederick Kluga 30, wife Josephine 30, as the son-in-law and daughter of Wencyl Kepl. They were living in Bethlehem. The WWI draft card for Frederick Kluge shows he was born June 24, 1890 and lived in Hellertown. A WWII draft card shows a Frederick Kluge was born June 10, 1889 and was living in Bethlehem Twp. Northampton County.
There are several sources you could check. Do you know when and where he died and is buried? If you don't Josephine's obituary might list the year he died (assuming he died before she did). The church they were members of may have something in their records.
Most likely they got their marriage license at the Northampton County Register of Wills Office. It may havedata on the parents. If he became a naturalized citizen he most likely applied at the Northampton County Prothonotary Office. His papers probably list when and where he arrived and where exactly he was born.
His obit and death certificate may have the parents' names and where exactly he was born.
Check with the Bethlehem Public Library and the Easton Area Public Library to see if they might have his obit. The Easton Library has an online index: http://www.eastonpl.org/obituary_index.htmhttp://www.eastonpl.org/obituary_index.htm