Depends on the mix.. It could be made with VG nic and VG flavorings, which means it would be 100% VG. Nomally, it's anywhere from 80-95%. Flavorings are usually in a PG base.
If you use a calculator like E-Liquid. You can select the MAX VG option. It will drop the PG from the selection list, and give you the ratios based on the amounts of each PG based liquid (NIC & Flavors) used.
If you're buying MAX VG from a vendor or store front. The only way to know for sure is to ask. Then hope they tell the truth, if they even know.