What should be the best mod for SEO? To generate sitemap and manage seo system for my website.
SEO and user generated content generally doesn't get along well. If you still want to give it a shot try the Optimus brave mod. It does what needs to be done for forums but do not expect for it to add any kind of regular static content SEO.
There are a couple of sitemaps, try searching the mod site (https://custom.simplemachines.org/mods/index.php?action=search;basic_search=sitemap)