Sharepoint - SharePoint Wiki Table of Contents
There is no OOTB capability in SP 2013 that will let you have a table of contents from a selected portion of content, however there are some nifty workarounds available mentioned below you can try it out.
Add navigation table to wiki page
SP 2010 workaround, should be valid for 2013
Recently I updated my Add navigation table to wiki page solution to support multiple levels and SharePoint 2013.
The new solution is a configurable jquery plugin and is documented in the blog post Revised: Table of Contents for Wiki Pages