Final answer:
A second dash should be placed after the word "honesty" in the sentence.
Step-by-step explanation:
A second dash should be placed after the word "honesty" in the sentence. The dash is used to set off an interrupting or parenthetical element, which is the phrase "and I say this with all honesty." This phrase provides additional information but is not necessary for the sentence to make sense. Therefore, the correct punctuation would be:
I believe - and I say this with all honesty - you are destined for great things.
Learn more about Punctuation in English sentences