Short answer: Generally an administrator account can access and read any file on the computer. To protect files, either remove all untrusted admin accounts except for yours or encrypt the specific files you need protected with your admin password. Another admin can reset your password, but not see it to unlock things like your keychain. Of course a new password for encryption is ideal if you don’t trust another admin.
There are certain files within your account that are encrypted and can not be read without your password.
The main file I'm thinking of is the "Keychain" which may contain your iCloud password and any other passwords you've allowed Safari (or other apps) to remember.
As an IT system administrator myself I would recommend not to store personal data on your work computer that you don't want anyone else to see.
The computer may have backup software that's backing up all files on the computer - including your iCloud Drive.
Also remember that if you're fired, the computer may be taken away before you have a chance to remove your personal files.