WordPress doesn’t have any sitemap natively. There is an ongoing project to include such a function in Core, see https://make.www.ads-software.com/core/2020/01/27/feature-plugin-xml-sitemaps/ but it may take some time before that happens.
However, any typical SEO plugin will happily generate XML sitemaps if you ask them to do it. So: enable XML sitemap in your SEO plugin and find its URL.
Next add a line like this into your robots.txt:
Sitemap: https://example.com/sitemap.xml
As you can see, this statement should include the full URL to your XML sitemap. It can be put before or after the current “User-agent” blob. The order is not important.
(Note that the search engines prefer sitemaps in the XML format, which includes some additional meta data about the entries. If you want to show a sitemap to your visitors, then a sitemap in html format is better.)
And the User-agent blob you showed looks ok. It just asks the crawler bots not to read pages under /wp-admin (which they hopefully wouldn’t be able to do, anyway).