Rather than asking how they might debate, why not debate them and find out?
I know exactly how they will debate. To claim to be agnostic, secular and humanist gives you the mindset of a 15 year old boy. There is an intense lack of nuance and intellectual maturity with such a philosophy. Teenage boys think the world is black or white. And are happy to identify with overarching theories and embrace them as their own with little understanding of how they translate to the real world. This is a group of people who have decided to surround themselves with people they agree with and close themselves off from those with other opinions. That is not a healthy social circle of people to meet in your first few weeks at uni.
They have deliberately chosen to identify with leftist ideologies. There is nothing Christian or conservative or centrist about them. They are not moderates. They are the mouth pieces for leftist professors who suckle from the state teat. These are the people who think Jeremy Corbyn is a good idea. They are not only dim witted ... they are dangerous in large groups. And they have created an organisation for the purpose of parroting these ridiculous ideologies in front equally impressionable, and might I add miserable individuals, who will nod along and agree with them.
Why would I want to address a crowd of people who are agnostic? Choose. What feels right? What does millions of years of conditioning make you believe? Why deny spirituality when you and everyone else has evolved to include it? Independently, no matter where on earth. Its a survival skill. Its stops nihilism. It stops suicide. It stops immorality and crime. It allows the building blocks of civilisation and cooperation. No group of people ever rose up ever to anything being atheist or agnostic. Choosing to believe in something is not a tough choice. Its outright obvious. I don't care what people believe ... it makes no odds ... animal gods, Islam, Christianity ... pick something. How can you take seriously a group of people that when asked "do you have a soul?" don't know the answer. Why would anyone want to spend a second of their lives in the company of people without souls? I have a soul. It makes me, me. It connects me to the universe and gives me an inner peace as demanded by my biology ... I am a spiritual creature ... I evolved to be like that. Anything else is a path to misery.
These people are too busy focusing on the truth. A truth they will never know anyway. And whilst they while away hours debating its pros and cons they miss the point. The point is not to believe the truth ... it is to believe whatever makes you happy. Whatever is in your best interest. Whatever improves your life. And agnosticism improves nothing. You don't take the red pill. That's no good to you. You don't get Neo super powers. You take the blue pill. Because it improves your life.
When you are sick, you have comfort.
When you are dying, you have faith.
When you are treated unjustly, you can ask for divine retribution.
When you are poor or enslaved or downtrodden, you have hope.
And when you are guilty ... you can receive forgiveness.
There is no upside to being right. And when you say you don't believe, you are powerless. Law follows religion. You say you don't believe and you want your state secular, then you get no protection. When the pay day lenders and debt companies appear ... you can't cry "usurers!". When politicians discuss removing debt forgiveness or allowing predatory gambling companies you can't shout "heresy!". When your government commits crimes that were banned for thousands of years ... you can't say shit. And all because you wanted to be 'right'. Being right, was the wrong answer. That's nuance. And you can't expect those with teenage brains to comprehend it. Discussing the shape of the earth with these people? Where would you even begin? They have far bigger problems.