The ability reads:

"Enemy ships at range 1 cannot add their range combat bonuses when attacking."

Does this mean any enemy ship at Range 1 of any of your ships cannot add that extra die? Or is it only when Zertik is at Range 1 of an enemy ship?

Enemy ships in Range 1 to Zertik don't get their Range 1 Bonus (against anyone). A Card text always refers to itself (or the ship it is attacht to in case of upgrades).
Otherwise the text should be
'Enemy ships at range 1 to a friendly ship cannot...'

The 'of you' is implied when it should be stated.

Ok thanks. My brother copied it with Thweek and was skeptical to how it works.