2 fast questions

Hello

1) When I add sitemap to my google search console, it appear "verfying, pending" and I check it later it disappear, is that normal?
2) I have a domain which I don't use, should I redirect it to my site? can this improve seo?

once the verifying goes away you should see it say how many pages were submitted or see an error.

Pointing the other domain will not help with SEO unless it was a domain that had links already going to it. But even then it would not help much.