How to export leads from Sales Navigator starts with LinkedIn's own answer: not as a file. LinkedIn's help page on exporting lead and account information says it does not offer an export from Sales Navigator into a CSV or XLS file, on any plan. What it does document depends on your plan, and the routes that move leads out at all go into a CRM.
What each plan gives you
On Core and Advanced, leads you save to a list stay inside Sales Navigator. Advanced adds a CSV upload, but it goes the other way: a file of companies into an account list, not leads out.
On Advanced Plus, CRM Sync opens the routes that write to your CRM. You can create a lead in your CRM from a lead's page, create and update contacts, and log your activity on the matching record. LinkedIn names Salesforce, Microsoft Dynamics 365, HubSpot, and Oracle Sales for CRM Sync.
No route on any plan moves a whole lead list or account list out of Sales Navigator.
How to read the helper
Pick your plan and the helper marks the routes you have, each with the LinkedIn page it comes from and the day we read it. Pick your CRM too, and it shows whether LinkedIn's pages name it for each route.
Watch the direction of each route. Several bring your CRM's records into Sales Navigator, and nothing leaves. Others only show Sales Navigator details on a record inside your CRM.
Paste a Sales Navigator search link and the reader lists each filter with its values, marked included or excluded, plus any keywords. The link is read in your browser tab and never sent anywhere. The filters are the part of the work you can always write down, for a brief or a CRM view.
What to do next
If your plan writes contacts to your CRM, start there. Whichever route you use, a work email you can send to is a separate job, and none of LinkedIn's routes finds one.
For a list of people with work emails, Oneprofile's people search filters by job title, seniority, location, industry, and company size, and finds work emails as you save. Counting matches costs nothing.