How to create Table of Contents in Keynote?
Assuming one is using Keynote 6 (OP did not state version used.), one way to create a Table of Contents or Handout is to use the Print dialog.

This can be printed to PDF for handouts.  One way to customize would be to create a duplicate copy of your presentation then edit the copy before printing the outline.

Edit After printing the outline to PDF, one can create a new slide at the beginning of the presentation and insert the PDF outline onto the slide.