Pristine MoS2 just refers to the fact that it's unmodified or not doped or altered in anyway. Pristine MoS2 can be the bulk material, or a few layers thick, or monolayer. The conductivity of the sample depends on the substrate and any defects from the fabrication. Fabrication techniques aren't perfect so vacancies are common enough and contaminants can substitute in the place of sulfur in the lattice. Oxygen is a common contaminant in MoS2 and there can also be contaminants in the sources used for CVD grown samples.

The bandgap type for pristine MoS2 depends on whether the sample is monolayer or not. Pristine monolayer MoS2 has a direct optical bandgap at around ~1.8-1.9 eV depending on the substrate. This is the signal you would see for the A-Exciton in optical techniques like PL. The electronic or fundamental bandgap is larger than this and is equal to the optical bangap(Exciton energy) plus the exciton binding energy binding energy.

The bandgap for MoS2 changes to an indirect band gap with a lower energy ~1.2-1.3 eV for bilayer and thicker samples of MoS2.

The band gap depends on doping and substrate and can be determined theoretically or through experiments. The optical bandgap can be determined from optical techniques(i.e. PL) or by Kohn-Sham theory in DFT. Electronic band gap values can be determined by Scanning Tunnelling Spectroscopy (STS) or GW calculations in DFT.

This paper discusses how substrates affect conductivity:

Article Origin of the n-type and p-type conductivity of MoS2 monolay...

And this paper uses DFT to calculate the optical and electronic bandgaps of TMDCs using a number of different approaches. Just be careful to pay attention to the technique used and whether they show the electronic or optical bandgap. Table 2 shows the experimental electronic bandgap from STS and the exciton binding energies. Table 3 seems to use optically acquired experimental bandgaps.

Article Electronic Properties of Bulk and Monolayer TMDs: Theoretica...

There are also plenty of other papers out there that explain the subject in more detail including the book "Two-Dimensional Transition-Metal Dichalcogenides" by Alexander V. Kolobov and Junji Tominaga.

Eoin Moynihan is right. In short, the difference between bulk MoS2 and a monolayer of MoS2 is reduced to two points.

1. This is a direct gap in monolayer and indirect in bulk material. This is due to the fact that 2 monolayers are included in the MoS2 unit cell. Therefore, its structural type is designated as 2H.

2. In bulk MoS2, interstitial insertion defects (intercalated atoms) are possible. They can play the role of donor impurities. Therefore, bulk MoS2 has n-type conductivity. In a monolayer, such defects are impossible.

Thanks for your answers