Based on my own personal research I believe the 2nd shooter was most likely by the AMPM (likely from an elevated point such as the roof) which is located ~300 yard to the north of the stage at the fairgrounds. The reasons for me focusing mainly on this location is due to the fact that it most accurately aligns with other evidence from that days events which I will list below.

1. The AMPM lines up with the ~250 yard radius of the 2nd shooter from the fairgrounds (as mentioned in the video above).
2. From the audio of the cab driver taken from just outside of the Mandalay Bay, the 2nd shooter appears to be quite far away (making the construction site and Oasis Apartment potential locations less likley), which most accurately lines up with the AMPM which is at the furthest possible location to the North of the Mandalay Bay (its the furthest point of interest from the 1st shooter, it covers the top half of the fairgrounds which the 1st shooter does not, it targets the fairgrounds from the opposite direction allowing for the attack to come from both the South (shooter #1) and North (shooter #2).
3. On police scanner transmissions during the event they mention that medics are reporting that they are being shot at in front of the entrance to the Tropicana, which is located ~250 yards from the AMPM, which is North of the AMPM within the 250 yard radius of the shooter (just like the fairgrounds is on the south side (~250 yards)). It is highly unlikely that those Tropicana shots to be coming from the Mandalay Bay (shooter #1), and is just as unlikely that those shots are coming from the other potential 2nd shooter locations (construction site/Oasis Apartments) all of which are much further South from the Tropicana then the AMPM location is.
   "Control 374 I got medics reporting they are being shot at, at the Tropicana"
   "Be advised that there is an active shooter at the Tropicana, active shooter Tropicana"
4. There are also reports of shooting take place near the Excalibur and New York New York Casinos which are even further North then the Tropicana on the opposite side of the Vegas strip, making it even less likely to be coming from the Mandalay Bay (shooter #1) as well as the 2 potential shooter #2 locations which are South of the fairgrounds (construction site/Oasis Apartments), while at the same time are within both line of sight, and at a closer range to the AMPM location.
   "Control 35-SD we have possible reports of shots fired inside New York New York"
   "We're getting a 415A, from the advisor that there was a shooter at the front desk. They have records at the 415A at New York there might of been an active shooter possibly coming down the escalator from New York New York to Excalibur"
5. There were also reports (via police scanner) of a 2nd shooting location taking place across the street East of the fairgrounds at Giles and Ali Baba, which again is highly unlikely to be from the Mandalay Bay (shooter #1) and is unlikely to be from either of the 2 Southern potential 2nd shooter locations (construction site/Oasis Apartments) due to distance from all 3, but again just so happens to be within the ~250 yard range of the AMPM location.
   "Control 224-IC confirming I have casualties at Ali Baba and Giles east of the Catholic shrine as well as in the Mandalay Bay, so we have 2 scenes"

Basically the AMPM location lines up as the most probable 2nd shooter location during the event due to it being the furthest possible point from the Mandalay Bay within the shooters radius (which matches the audio evidence), allows for an attack from both sides of the fairgrounds (which makes sense if your going to do a 2 shooter event to maximize damage and minimize escape points), allows the 2 shooters to cover the entire fairgrounds with their attacks (shooter 1 covers the Southern half of the fairgrounds from the South while the 2nd shooter covers the Northern half of the fairgrounds from the North), it is one of the only locations possible that would allow for shots to be fired at not only the fairgrounds, but also at the medics near the front of the Tropicana (as reported via police scanner multiple times that night), is also the most probable location for shots to be reported at the Excalibur and New York New York (has line of sight with both, is within reasonable range of both, by far more then any of the other potential locations), and is within the 250 yard range of the Giles/Ali Baba intersection where further casualties are reported (via police scanner).

Just my 2 cents....