If you were in an elevator free-falling 100 floors, and you jumped up, one inch from when the elevator hit the ground, would you be safe?

The normal office building floor is from 2.7 to 3.3 metres.

For your safety let's assume your office is 2.7 metres (this is a floor to floor measurement).
The acceleration of free fall is 9.8 m^2
Your initial V = 0

From the formula V2^2= V1^2+2as (ie final velocity^2 = initial velocity^2 + 2 times the acceleration by the distance.

So V2^2= 0 + 2X9.8X(100*2.7)
V2^2 = 5292
V2 = 72.73 m/s

This is your speed relative to the ground.

The highest standing vertical jump according to Guinness records is 5'3", approximately 1.5748 metres. He would have needed to have an initial speed of 5.556 m\s to reach the top of the pile at which his velocity would be close to zero.

So relative to the enclosed lift when you jump up, you are travelling upwards at 5.556.

Sadly relative to the ground, even at your fastest, you are travelling (72.73 - 5.556), that is,
67m/s towards the ground.

That is a speed of 149.867 mph or 241.2 km/h.

Best of luck.