How can I use session variables in a report created with the Forena module?
I'm not (yet) sure about this one, because of the "session variables" that aren't clear enough to me (yet) ... Below are a few techniques (features) that you may want to consider to get it to work.

1. Using JavaScript and/or Skins

A possible solution "might" be to think of some technique you can implement via a JavaScript. And then make that JavaScript available via what in Forena is called "skins" (used for e.g. theming a report, like to enable the 'DataTables' plugin if you want, etc).

There are some "interesting" issues in the Forena issue queue with some great examples (ideas) of things you can do (add to Forena) via JavaScripts and/or Skins. HEre are a few of them:


Using the dataTables plugin to format reports, via an appropriate "skin".
Making table headers sticky, note the comments nr 8 (using Drupal Behaviours) and nr 10 (adding some JavaScript library).


2. Specifying Report Parameters as part of the URL

Report Parameters are similar to using arguments in Views. You can specify them as part of the URL, by first adding a ?-mark, followed by the name of the report parameter, a =-sign, and then the parameter value. So something like ?state=VA that you append to the report URL.

To see it at work in the demo site, try this example which uses ?state=VA (watch the URL of it also). Then change the end of the URL to something like ?state=IL,  ?state=CA, etc. To be complete, you can also specify multiple parameters (+their values) in an URL.

So if you have a way to massage those session variables in a such string added to the URL, then the answer to your question is something like "pass them as report parameters via the URL".

3. Other approaches

If what is above won't work, then please add more details about those "session variabes" (so that I can refine/rework my answer accordingly).

And if we don't find a real answer, then its time to experience the "support" that comes with Forena, via its issue queue on D.O. ... After all, keep in mind that I'm only a co-maintainer of this module. When I'm stuck (or out of Forena-inspiration), I escalate such questions/issues to David (the module owner and creator or Forena).