Template Toolkit debugging can be done with the DEBUG option. The TT docs on Template Options (Runtime) detail the option. I'd give examples to help, as I feel the docs are a little sparse as to implementation, but I've never used DEBUG. Sorry!

In fact, what I usually use is TT's Dumper module to find out what's being sent to my template from my code, like:

[% USE Dumper %]
<hr />
[% Dumper.dump_html(chunk_of_data_that_isn't_working) %]
[download]

That might work well for you. Does it at least give you ideas?