Corporate Jet pilot reported they descended below the Glideslope and received a Ground Proximity Alert while the Pilot Flying was utilizing the Enhanced Vision Flight Vision System for practice during daylight clear weather conditions.

Narrative

ZZZ ILS Z XXR During ILS Z approach to ZZZ Runway XXR; the G650ER was slightly below GS just after passing DH; inbound to land on Runway XXR. Crew was likely task saturated while practicing a 'simulated' EFVS (Enhance Flight Vision System) approach to TD/Rollout in VMC and may have lost some situational awareness resulting in EGPWS Mode V activation. Crew had recently completed initial EFVS TD/RO simulator training course and annual recurrent training and sought the training benefit/objective of 'real-world' application of newly learned procedures; practice somewhat confusing call-outs; and actual decision making in a live environment; given the opportunity of good weather and somewhat familiar airport. One interesting takeaway is that it is rather confusing to do EFVS simulated procedures in VMC/daylight while simulator training is done in simulated LIFR/night conditions.After aircraft passed DH; and; as PM may correctly recall; on a normal descent profile; the PF became slightly low on GS while referencing HUD 3.0 degree down FPA guidance. PM (self) did not detect the initial GS deviation as he was focusing too much awareness on identification of 'EVS Runway' lighting which takes place at 100' barometric above TDZE. *Note: Runway lights were not illuminated/daytime/VMC. GPWS Mode V 'Glideslope' audible warning sounded and PF took immediate corrective action. A normal landing followed. Not much thought had been given at the time as there was no perception of hazard by the crew during debrief. Several other interesting/distracting events (consistent with normal ops in the [metro] area) occurred earlier in the flight including a TCAS TAs during the ZZZZZ. ZZZZZ1 SID and just prior to commencing GS capture on ILS Z XXR. PM recalls delayed automated capture of the ILS Z XXR GS about this same time during the earlier stage of the approach. PM does not recall at this point in time (11 days later); if the A/P was coupled/re-coupled.