I believe its the hose from the fuel filter with the quick disconnect fittings on each end. Its a hard plastic tube, you have to cut and splice in a fitting for the pressure sender. Another option is get a big line kit between the filter and pump that has provisions for a sending unit. The banjo bolt on the pump I believe is the return line.
On my truck I put a banjo adapter in the feed line on the back of the fuel filter since I have 2 micron filtration back at the fuel tank and the filter on the engine is 5 micron. I am sure the filter at the tank would clog first so I feel fairly safe putting the pressure fitting there, probably not ideal but my truck is stock and fuel pressure gauge is mainly for monitoring the filters.