First of all user story writing does not need domain knowledge. It involves the identification of different user roles relevant to your project. All user stories are written from the perspective of a user type.wanted to understand how to approach/ get into user stories on a new domain/ product/ industry where we have no prior experience/ understanding.
(Personas / Market research some techniques used commonly but as a new PO how to make sure we do the right things in the right way.)
So rather than focusing on the technicalities of a domain, it needs the engagement of those who can share information about expected features and which user roles used those features.
So in summary involve those (mainly customer) -
Who can give information on the user roles who will interact with or use the solution?
Then you discover how different user roles prefer the solution to behave?
user stories need your stakeholder engagement abilities not domain knowledge abilities.