Exposure meter does not represent any value while exposure is under exposed, why this is happening? How can we check exposure value in manual mode?
Although the settings you have selected are far too dark for the lighting environment, that is not why you see no value on the "exposure meter."
... exposure meter doesn't show any value, why?
Because that's not the exposure meter you are seeing displayed. It is the 'Exposure Compensation' value currently selected. Since there is no selectable 'Exposure Compensation' value when shooting in Manual exposure mode with a specific ISO value selected, there's no 'EC' value to display.
Your photo shows the LCD displaying the 'Shooting Settings' screen. This screen shows you what settings are currently selected for the camera when metering is not active. Since there is no exposure compensation setting that can be entered when using 'Manual Exposure Mode' with a specific ISO value, there would not be any indication on that line when metering is not active, even if your exposure settings were exactly spot on.
The [INFO] Button settings and the 'Shooting Settings' screen are covered on pages 450-451 of the EOS 80D Instruction Manual.
If you were in P, Tv, or Av exposure modes, your entered Exposure Compensation value would be displayed on the -3 to +3 scale, even if the current lighting conditions were out of range for the selected ISO and Tv/Av selected. The graphic on the right in the image below is an example of the 'Shooting Settings' screen when the camera is in Program exposure mode that shows an 'Exposure Compensation' value of '0'. No Av or Tv information, both of which are selected by the camera in P mode, is displayed in the example because metering is not currently active. In Tv or Av modes the Tv or Av value selected by the user are displayed in the two boxes on the top line that are between the 'P' and the 'ISO Auto' icons. The remaining setting left up to the camera is left blank until metering is active. In P, Tv, and Av modes, even when metering is active, the scale still shows the selected EC value. If the current user selected Av/Tv/ISO settings are out of range for the camera to be able to select proper values of the remaining exposure parameters (whichever part of Av/Tv/ISO the user has left up to the camera), the camera's selected values will blink, but the exposure scale will continue to show the selected setting, rather than a meter value.
Setting 'Exposure Compensation' is covered on pages 200-202 of the EOS 80D Instruction Manual.
If the meter, rather than the non-existent 'Exposure Compensation' setting when shooting in Manual exposure mode were displayed, there would be an arrow (or possibly a blinking line¹) to the left of (or beneath¹) the '-3' position to indicate the selected settings were more than 3 stops too dark for the current lighting environment.
But the actual meter reading can only be displayed on the 'Shooting Settings' screen when metering is active. The easiest way to activate metering is to half-press the shutter button. If the half press (or other button used to activate metering, such as the AF-ON button) is not held, metering will time out in a few seconds (this value can also be customized using the camera's settings menu). If metering is active and the selected settings are out of range of the -3 to +3 Ev meter scale, the vertical bar underneath the extreme will blink or an arrow will be displayed just past the last value.¹
¹ I don't have an 80D to test. My 5DIII (2012) and 7DII (2014) show an arrow just to the left of the '-3'. My 7D (2009) shows a blinking vertical bar directly beneath the '-3'. My 5DII (2008) and 50D (2008) and Phillip's 550D (2010) show the blinking line beneath '-2' of their -2 to +2 scale. Since older cameras released up to about 2011, regardless of the model line - Rebel, x0D, 7-series, 5-series, etc. - to which they belong, use the blinking line and newer cameras since 2012 use the arrow, my money is on it being a constantly on arrow when metering is active for the 80D released in 2016.
The exposure meter isn't showing anything because you're massively, massively underexposed - you've selected the fastest possible shutter speed, the narrowest possible aperture and the lowest possible ISO - i.e. the very lowest exposure the camera can manage. And then you're in a dark room - you'd be underexposed on a sunny day.
Get the exposure somewhere vaguely in the right ballpark (start from the program mode settings) and then you'll see something on the meter.
... exposure meter doesn't show any value, why?
Because that's not the exposure meter you are seeing displayed. It is the 'Exposure Compensation' value currently selected that is being displayed. Since there is no selectable 'Exposure Compensation' value when shooting in Manual exposure mode with a specific ISO value selected, there's no 'EC' value to display.
For more detail, please see this fuller answer.