Are speeds like Vmbe,Vmu calculated before each flight? and are they ever displayed/marked on the ASI?
Following a rejected takeoff, brake energy will be calculated (and may be seen in some systems as brake temperatures), and will have a direct impact on turn around times, the ability to taxi, any replacements or inspections that are required, etc.
Brake energy numbers aren't depicted on the airspeed indicator. The numbers you're interested in are decision and safety speeds, and flap speeds: operational numbers.
would the captain take controls and continue takeoff?
im assuming by the time i report and he takes controls the plane would continue acclerating..
As the pilot flying, you're going to continue the takeoff unless the captain elects to reject the takeoff.