Crossword puzzle clue "can be found"

"Can ___? Can I? Can I?"

"Can I? Can I? Can I?" e.g.

Where "Lost" can be found

Nickname of the man (born 2/12/1809) who gave the address at 18A, issued the 28A/45A, was the first elected president of the 60A Party, and whose name can be found in this puzzle's main diagonal

Dolphins can be found there

Early, or a hint to where each half of each starred answer can be found

Secret's source ... that can be found four times in this puzzle

Somewhat suspect (and a hint to what can be found by connecting the circled letters in alphabetical order)