Est Pre-Boil Volume and Gravity

I wonder if the Pre-boil Volume and Gravity is at 20 degree or at 100 degree. Thank you

Gravity reading should be measured at 59 or 60f (15C or 15.5C).  Any other temperatures must be adjusted for temp. 

From my observation the pre boil volume is the volume of wort at 100 ° C (not converted for temperature) and pre boil density must be converted to the calibration value of your hydrometer.

You should take your PBG (pre boil gravity) just as the kettle comes to a boil. To be useful, you really need to use an ATC refractometer. Just as the wort comes to a boil,  it will be uniformly mixed to eliminate bad readings due to temperature stratification, which is exactly what happens if you try to measure following the sparge. This will be your PBG, say 7 gals, which is the amount of wort extracted. It also won't be expanded 4% until the hotbreak when the volume will increase to 7.28 gals. In my world, this will evaporate to 6 gals in 1 hour. Shrink to 5 .75 gals when cool. Leaves 1/2 gal trub in kettle and puts 5 1/4 gal into primary. My final numbers: OG and IBU are based on the 5.75 gal net yield. If I leave more or less trub in kettle, it doesn't matter. Sample problem: 10 lbs x 27 PP = 270 pts. 270/7 gal=39 PPG PBG. 270/7.28 gal=37 PPG BG. 270/5.75 gal=47 PPG OG.
Why do we care? Wouldn't it be nice to know that your extract yield assumptions were close enough so you didn't have to recalculate your hop additions. If your MEE was 60% or 85% and you planned on 75%, you will clearly need less or more hops to hit your desired IBU target, which in turn affects malty/bitter relationships.
As always, YMMV.