There is an achievement category named "Trading pass". You need to complete all the achievements in that category to unlock your trading pass and thereby enable trading. Please check individual achievements for more details about specific requirements.
Do I have to get a new trading pass if I already have the old version?
No, trading passes earned before Habbo 2020 are equally valid as the new versions. If you have an old trading pass, you can continue trading with it. You can also complete the new trading pass achievements if you want!