Your father, Ludwig Joseph Knapp, filed for a corrected birth certificate. On the original his last name was recorded as Knaps. It looks like the correction changed it to Knapp. The original was recorded in 1943, so it must have been a delayed filing. In 1943 his uncle, Paul Bartsch, filed an affidavit to prove his birth date. You can view the correction form on familysearch.org. You might also want to order a copy of his birth certificate to see if it has any information on his father.
Fritz is usually a nickname for Fredrick. Here's a possible match from the 1900 census. I can't find them in 1910.
1900 United States Federal Census Name: Fred Knopf [Fred Knapp] Home in 1900: Justice Precinct 1, McLennan, Texas [Golinda, McLennan, Texas] Age: 18 Birth Date: Jun 1881 Birthplace: Germany Race: White Gender: Male Immigration Year: 1896 Relationship to head-of-house: Son Father's name: Frederick Knopf Father's Birthplace: Germany Mother's name: Friderka Knopf Mother's Birthplace: Germany Marital Status: Single Occupation: View on Image Neighbors: View others on page Household Members: Name Age Frederick Knopf 54 born Germany Friderka Knopf 48 born Germany Fred Knopf 18 born Germany Albert Knopf 12 born Russia Malmerine Knopf 14 born Russia Betta Knopf 8 born Russia Adolph Knopf 6 born Canada H*Lda Knopf 4 born Canada