Is attitude obtained by AHRS or GPS?
The TruTrak Gemini gets its altitude info from the pitot/static not GPS.
Can this TruTrak Gemini PFD be used as a primary instrument in a certified aircraft?
No, these are not certified. They are intended for experimental aircraft only. Not for use in certificated aircraft.
Does the Gemini PDF need an external GPS hook up?
Per the Manufacturer, the Trutrak Gemini PFD needs to be connected to a gps.
I have a Garmin 296 driving the track function of my Navaid AP-1. Does the Garmin 296 have another output that I can use to provide GPS info to the Gemini PFD?
Per Garmin, You can split the data line on a Garmin 296 to output to up to three devices.
Can the Trutrak Gemini PFD be used as a back-up inst on a certified aircraft? Why is a GPS required for this instrument?
As the Trutrak Gemini PFD is not certified, it is intended for experimental aircraft only. The GPS is required for tracking and heading reference.