Yes, you can output the topic flow to a png by opening it in VA Designer, then clicking the camera button on the top right corner (then right click > save image after it opens in a new tab):
This is the best, easiest, and (I'm fairly sure) only way to export a topic for documentation/requirement purposes. This exemplifies the importance of having good, clear node naming conventions which is the single best thing you can do: use plain, concise English, avoid abbreviations (unless maxed out character limits), and name all your decision blocks and decision outputs (don't keep the defaults). Personally I avoid special characters in input nodes so that the variable names are short and clean, but decision blocks and other outputs I use special characters (question mark is helpful for decisions) to ensure those are descriptive and clear.
The only other tip I can give you working with customers/topic SME's is to have a live meeting with them and walk them through the entire flow step by step in VA Designer so they can see the wording and specific settings.
