For reference, you can see the entire list of questions here.
You can also see other posts where I've answered questions from theists here, here, and here.
Today, I'm tackling the section helpfully labelled "TRUTH". Here we go.
1. What or whom do you consider to be YOUR chosen intellectual starting point, your supreme authority for knowledge, your final standard for truth? Why?
This is a complex question. The nature of knowledge and truth have been the subject of philosophical inquiry and thought for, quite literally, millennia. In my life today though, I would say evidence.
I don't believe truth can exist separated from the evidence for it, so when I am examining my own knowledge and truth, I measure it up to the evidence. I try to do this with all of my beliefs and assumptions, although I am not as good at this as I hope to become as I continue to grow my skeptical thinking.
2. Would you consider turning skepticism on itself and examine your own assumptions?
I have to be honest: this is a silly question. There's not many silly questions out there, but this is one of them.
Skepticism is a way of thinking. You should (in an ideal situation) apply that way of thinking to everything, including skepticism itself and, yes, your own beliefs.
As human beings, we aren't always the best at this because we're driven to confirm our own beliefs and way of thinking. We want to be right, no matter what, and that makes it hard to remember to subject our own beliefs to such scrutiny. I know I am guilty of this from time to time, but overall, yes, I'm more than willing to subject my own assumptions to skepticism. That's what skepticism means to me.
3. If God exists, could Christianity be exclusively true?
The short answer is: yes.
The longer answer involves the "folly of the lottery ticket".
I first read about the folly of the lottery ticket in Atheist Mind, Humanist Heart: Rewriting the Ten Commandments for the Twenty-first Century by Lex Bayer and John Figdor.
Bayer and Figdor liken picking any of the many religions to picking a lottery ticket. Take last week's huge Powerball drawing--$1.2 billion. There was a 1 in 292 million chance that any given ticket would be a winner. If you were holding the ticket, you might hope it was a winner--but you'd probably not start spending the money quite yet.
In the book, they explain it like this:
A key concept here is that you can't tell what a winning ticket looks like until the results are announced. Each lottery ticket can have many characteristics: one could be dirty, another might have a torn edge, another might be creased, the numbers on one could all be odd, and another even--but none of these characteristics have any meaningful connection with the likelihood of that ticket being a winner. So to believe with any kind of certainty that yours is the winning ticket is to fall into the "folly of the lottery ticket." 
So assuming that your ticket is the winner is a stretch. Any ticket might be a winner, but it's far more likely that the ticket you are holding is not.
So while yes, Christianity could be that winning Powerball ticket, it's far more likely that it isn't.
This was a short segment. However, the questions were pretty profound, in my opinion. Again, I like the way that the question started by asking about the other person's (in this case, the nonbeliever's) frame of reference. I think that's a great place to start a dialogue.
The other two questions were kind of duds for me. I feel like the second one made the assumption that skeptics and atheists aren't willing to be skeptical about their own beliefs, and while that's true sometimes, it's not something you can generalize to the entire community. The third question seems like someone really went "Eureka! I've got them now!" but it's not a "gotchya" in the slightest for me. It's actually something I've spent a lot of time thinking about before and after acknowledging that I am an atheist, so the answer comes easier than my answer to most questions like these.
I do appreciate still how this author at least tries to dialogue. Sucks to know that they are only doing it to try to convert us, because I feel like an exchange with some of these questions could be really meaningful and interesting.
Anyway, feel free to leave your answers in the comments. I look forward to seeing other thoughts on these three.