I became a better UX Writer once I started asking questions.
My first month or so, I was afraid to ask anything; I thought it would expose me as not knowing enough, both about the product and writing in general.
I told myself I was just trusting the designer to know the details, but this is a cop out: designers should know the product and flow like the back of their hand, but they're human. Sometimes it takes more than one pair of eyes to see an edge case; and even if they did "catch" everything, copy needs to work for all use cases, not just one.
If you don't know what's going on, you can't write good copy. Text doesn't live in a bubble. A good UX Writer is just as involved in the context as the text itself, and that means collaboration with designers, PMs, and any other relevant stakeholders.
Not sure how to collaborate with your designer? Ask about anything you don't understand. If you don't know what happens when a certain button is clicked, chance are the user won't, either. But for more specifics:
Which screens come before the flow? After?
Are there other routes the user could have taken to get to this screen?
What does the user expect to accomplish here?
Have we thought about error messages and prevention, confirmation modals, etc.?
Can we be more specific with certain messages? Is there copy present that doesn't need to be here?
💡Pro tip: UX Writers can sketch, too. The layout of content is just as important as the content itself. Sit with your designer and sketch out different ways to arrange the flow; chances are they'll know a lot more about spacing and other visual details than you, but playing around together on a piece of paper or in Figma can be a great way to brainstorm.
You can't collaborate without an open flow of communication and ideas. Remember: the only dumb question is the one you don't ask.