You can either double click on the record to open up the record's details or you can click the Mkto ID to open up the same area. The Activity Log is the last tab.
I'm trying to figure this out, too. I was able to identify the leads who filled out a form, find their lead activity log, and click on the ID column for that row to show detail--but all I see in the Form Fields section is lines of code. I also tried to create a view for the smart list, but do not see the form or any of the fields listed among the optional columns.
When you click a Filled Out Form event, as Josh and Jeff mentioned, you see the raw form post data.
Though I use this area for debugging quite a bit, I'm not clear on why you want the raw information rather than the lead fields themselves.