Prashant's interpretation is correct. I will add a few words to explain why "go over" has the meaning he described. To understand the meaning, you need to know that "over" acts as an adverb, not a preposition, in the expression "go over". That is what led you astray. You thought it was a preposition and that "afternoon" was the object of the preposition: "over the afternoon". That is completely wrong. Instead, "over" is an adverb that modifies the verb "go". Here is a sample sentence in which "over" acts as an adverb, not a preposition: "Did you see how that bird went over?" ("went over" = "flew by") Answer: "Yes, I did see it. It was absolutely amazing!" If you understand that example, then you can understand the speech example: "How did your speech go over?" Answer: "It was fabulous. Everybody loved it."

Your interpretation is slightly off. Here's the corrected explanation: The sentence "I wonder how my speech will go over this afternoon" means: "I am curious or uncertain about how my speech will be received or perceived by the audience this afternoon." It does not mean that the person is looking for a way to finish their speech; instead, it reflects their thoughts about the audience's reaction to their speech. Here's your corrected explanation: "I am wondering how my speech will be received this afternoon. The speaker is curious or concerned about the audience's reaction to their speech."

The sentence: "I wonder how my speech will go over this afternoon." means: The speaker is curious or concerned about how their speech will be received or perceived by the audience this afternoon. They are not talking about how to end the speech but rather about the audience's reaction—whether it will be positive, negative, or neutral. Your interpretation is not correct. It does not mean they are thinking about how to finish the speech. Instead, "go over" in this context refers to how something is accepted or understood.

How will it be received by the audience / his or her colleagues.

Your interpretation is almost there! Let's break it down: "I wonder how my speech will go over this afternoon." "I wonder" expresses curiosity or uncertainty about something. "How my speech will go over" means how well or how effectively the speech will be received by the audience. "This afternoon" refers to the time the speech will take place. Meaning: The sentence means that the speaker is curious or unsure about how their speech will be received or how well it will go when they deliver it this afternoon. It doesn't specifically refer to the end of the speech or how they plan to finish it. Your interpretation ("I'm guessing how my speech will end this afternoon") is a bit off, as the sentence focuses on how the speech will be received, not how it will end. Let me know if you need further clarification!