How do I find version of Intel graphics card drivers installed?

You can view all your video adapters with the lspci command

lspci -k | grep -EA3 'VGA|3D|Display'
  |    | |   |    |        \- Only VGA is not good enough,
  |    | |   |    |           because Nvidia mobile adapters
  |    | |   |    |           are shown as 3D and some AMD
  |    | |   |    |           adapters are shown as Display.
  |    | |   |    \---------  Print 3 lines after the regexp match.
  |    | |   \--------------  program for searching patterns in files
  |    | |                    (regular expressions)
  |    | \------------------  pipe used for passing the results of the
  |    |                      first command (lspci -k) to the next (grep)
  |    \--------------------  Show kernel drivers handling each device.
  \-------------------------  utility for displaying information
                              about PCI buses in the system and 
                              devices connected to them

The output will be something like this:

00:02.0 VGA compatible controller: Intel Corporation HD Graphics 620 (rev 02)
    DeviceName:  Onboard IGD
    Subsystem: Dell HD Graphics 620
    Kernel driver in use: i915

01:00.0 3D controller: NVIDIA Corporation GM108M [GeForce 940MX] (rev a2)
    Subsystem: Dell GM108M [GeForce 940MX]
    Kernel driver in use: nouveau
    Kernel modules: nouveau, nvidia_drm, nvidia

As you can see, I have an Intel GPU and an Nvidia GPU. The Intel GPU is using the i915 driver and the Nvidia is using nouveau. You can check this in the Kernel driver in use: section of the output.

The standard Intel driver is a built-in part of 1) the kernel, 2) the Mesa 3D graphics library. Therefore it does not have its own versioning; as long as you have the latest kernel and Mesa, you have the latest Intel driver as well.

To see your active kernel version, use uname -r or dpkg -l | grep linux-image.

To see your active Mesa version, use glxinfo -B or dpkg -l | grep mesa.

Within Xorg, interfacing with the Intel driver might be handled by the xserver-xorg-video-intel module. Again, use dpkg -l to check its version (and note that the package might not be present, in which case Xorg accesses the same Intel driver via the "modesetting" interface).