If you know the approximate original file types (e.g., lost photos), you can also use (free, from CGSecurity) – it ignores CHK extension and carves files by signature directly from the disk.
While not exclusive to CHK files, (by the makers of CCleaner) can scan a raw drive and recover original file structures. However, it requires you to run it before CHKDSK converts your data to CHK files. chk file recovery registration code free high quality