Note that the WPCS standards for PHPCS are not “official”. I am one of the maintainers, and all that we can do is to do our best to match the standards that WordPress suggests. In this case, I’m unsure how you would escape the output from wp_oembed_get(). The function may indeed need to be escaped as the returned value is passed through several filters, and may actually contain raw unvalidated HTML from the oEmbed provider.
If you trust the oEmbed provider, the filters, and your network connection, one option would be to just whitelist this line of code, like this:
echo wp_oembed_get( 'https://www.youtube.com/watch?v=someidhere' ); // WPCS: XSS OK.
However, if the URL is user supplied or something, and you don’t think it is safe to trust the possible provider(s) in the context of your plugin, then you might want to take a look at the raw value being returned by wp_oembed_get() and see about crafting a whitelist of HTML elements and attributes to expect, to pass to wp_keses().
Note that obviously the WordPress core developers feel that the risk from oEmbed discovery isn’t very great, and so users can paste links into posts and they will be auto-embedded. WPCS is simply super-paranoid about these things, and it is up to the developer to know when it might be OK to take its advice with a grain of salt. One of the most strict followers of the late-escaping policy is wp.com VIP. Looking at its developer documentation however reveals that it does seem to allow the use of wp_oembed_get(), though it suggests the use of its custom implementation, wpcom_vip_wp_oembed_get(), for added caching features.
So in the end, you probably shouldn’t be too worried about escaping wp_oembed_get(). If you raise the issue on WPCS’s GitHub repo, the function might even get added to the default whitelist.