There is a NMEA WAGO connector inside the FCV295 that would be used for interfacing with your Garmin. If you want to display GPS position on the FCV295, then wire the Garmin Out+ to J2 #3 (In+) and the Garmin Out- to J2 #4 (In-). This connection will allow up to 20 waypoints (name & Lat/Long) to be stored within the FCV295 itself when the MARK key is pressed.
If the Garmin accepts the TLL sentence, J2 #1 (Out+) can be connected to the Garmin In+ and the J2 #2 (Out-) can be connected to the Garmin In-. If it does and the 4-wire connection is made, then when MARK is pressed, a waypoint/quick point will be placed on the Garmin plotter screen.
Setup on the FCV295:
Display position data: Menu-Data-Data Box 1, then turn on "Position"; Menu-Data-Nav Data, select "GPS"
NMEA information: Menu-System-NMEA, choose your NMEA version; select NMEA Port "In/Out"; select NMEA Output "On"; and TLL Output is set to "TLL"
This information should provide everything needed to interface the equipment.