There's a bug filed about this: https://bugs.chromium.org/p/chromium/issues/detail?id=158372
Original Answer (but see the update below)
What works for me is
wmic datafile where name="C:\\Program Files (x86)\\Google\\Chrome\\Application\\chrome.exe" get Version /value
It prints
Version=67.0.3396.99
surrounded by some blank lines.
There are some other suggestions in the bug comments, like querying the registry.
Update
Someone from the Chromium team posted this "totally unsupported" batch file in the bug comment thread:
@ECHO OFF
:: Look for machine-wide Chrome installs (stable, Beta, and Dev).
:: Get the name, running version (if an update is pending relaunch), and
:: installed version of each.
FOR %%A IN (
{8A69D345-D564-463c-AFF1-A69D9E530F96},
{8237E44A-0054-442C-B6B6-EA0509993955},
{401C381F-E0DE-4B85-8BD8-3F3F14FBDA57}) DO (
reg query HKLM\Software\Google\Update\Clients\%%A /v name /reg:32 2> NUL
reg query HKLM\Software\Google\Update\Clients\%%A /v opv /reg:32 2> NUL
reg query HKLM\Software\Google\Update\Clients\%%A /v pv /reg:32 2> NUL
)
:: Look for Chrome installs in the current user's %LOCALAPPDATA% directory
:: (stable, Beta, Dev, and canary).
:: Get the name, running version (if an update is pending relaunch), and
:: installed version of each.
FOR %%A IN (
{8A69D345-D564-463c-AFF1-A69D9E530F96},
{8237E44A-0054-442C-B6B6-EA0509993955},
{401C381F-E0DE-4B85-8BD8-3F3F14FBDA57},
{4ea16ac7-fd5a-47c3-875b-dbf4a2008c20}) DO (
reg query HKCU\Software\Google\Update\Clients\%%A /v name /reg:32 2> NUL
reg query HKCU\Software\Google\Update\Clients\%%A /v opv /reg:32 2> NUL
reg query HKCU\Software\Google\Update\Clients\%%A /v pv /reg:32 2> NUL
)
That should probably be seen as the right way to go for the time being.