Are the parts of text that appear on a wiki page as a result of Transclusion considered for that page's on-page SEO? Or for purposes of on-page SEO would it only appear as {{:Example_article}}. Thank you.
Topic on Project:Support desk
Transclusion displays the contents of another page or template where they're used. That has nothing to do with SEO (if by SEO do you mean Search Engine Optimization, of course)
So when search engine crawlers are checking a page for keywords they will not see the keywords in transcluded text, and will instead see "{{:Example_article}}"?
Search engines see rendered text, not wikitext, just like your visitors.
Perfect. Thank you! :)