Asking questions first and not making assumptions is just one characteristic I expect of any good designer. It's our job to listen to the stakeholders to understand business goals. It's our job to listen to our users to understand their needs. And it's our job to ask questions to explore those goals and needs. It's also important to be able to ask questions strategically, to probe ideas or strategies, especially when you think there may be a better approach.
Curiosity goes hand-in-hand with asking questions. Curiosity is what leads to innovation. It's just about asking stakeholders and users questinos, it's about questioning your design decisions and asking, "what if we try this?", or "what would happen if..." and being open to exploration.
Finally, a question I like to ask myself often is "How can I best provide value right now?". It's important to interrogate your own methods and work to make sure opportunities to improve aren't being overlooked. "Is there something else I could be doing right now that would be provide more value?"