Short answer: No, there's currently no way to leave a note, comment, or question on a section for the owner; you'll need to reach them directly.
What's actually there
Each section you've been assigned only contains its own fields, uploads, and toggles. There's no comment box, note field, or question thread attached to a section, so anything you type only ever fills in the section's own data.
Note: This applies across all nine sections. Even sections with a free-text field, like Financials' context box, are answers to that section's own question, not a message thread to the owner.
If you have a question about your work
Since there's no in-app way to flag something to the owner, reach out the same way you'd contact them about anything else at your firm, for example email, chat, or in person.
Tip: If your question is about what a field is asking for or which section you're responsible for, check Your assigned work first. It may already answer what you need.
If you have a question about the portal itself
For anything about how the onboarding portal works, get in touch with the VLV team directly rather than trying to leave a note inside a section.