Answer:
His own name along with his father's.
Step-by-step explanation:
Oscar Wilde's "The Importance of Being Ernest" follows the comical romance of Jack "Ernest" Worthing and Algernon. The story deals with themes of class, society, belonging, morality, marriage, love, etc.
After Jack had proposed to Gwendolen, and Algernon had also proposed to Cecily, the two men were embroiled in a 'fight' to get the name "Ernest" as this was the name they had given to their respective fiancées. After they had gone over and rediscovered that they were actually long-lost, misplaced brothers, they decided to find out their father's Christian name.
Referring to the Army List, Jack discovered that their father's name was the same as his own- "Ernest".
Thus, the correct answer is the third option.