I am using a different domain for some ads to track how many people access the main site through this domain.
How can I see this in Google Analytics?
I have DOMAIN A (on the ad) redirecting to DOMAIN B (main site).
You need to change the redirect so that it adds UTM parameters. Instead of:
http://domaina.example/ -> http://domainb.example/
Use the Google Analytics Campaign URL Builder to build your final URL something like:
http://domaina.example/ -> http://domainb.example/?utm_source=the-global-times&utm_medium=print&utm_campaign=2019-push
That way your customers will be able to type in the simple short URL and Google Analytics will get the data it needs to track your campaign.