Welcome to the forum!
I've not got any experience myself but from what other people have told me over the years, you can expect a mixture of driving/driving rules questions plus general work experience, customer service scenarios, etc. Nothing that would surprise or trick you that I know of.
Is your DCPC just from periodical training or did you take the initial DCPC when you passed your LGV test? I suspect that you will need to do the whole lot again for your PCV...
There is an expert knocking about on here who will be able to answer that question more accurately if he pops by...