Per my test, we can view or cancel an alert for another person on SharePoint via site settings>User alerts under Site Administration:
In addition, please check the spam folder of gmail, alert emails from "******@sharepointonline.com" will be redirected to gmail spam folder by default:
As a workaround, we suggest you create a rule in gmail to avoid it, try as following:
1.Click settings>see all settings in gmail page:
2.Navigate to Filters and Blocked Addresses option and create a new filter as shown below:
3.If the from address is ******@sharepointonline.com, Never send it to spam:
4.After that, the new alert email will appear in the inbox:
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