How to see SES usage for domains?

I recommend taking a look at this documentation for Setting up Amazon SES event publishing. You can publish SES events to CloudWatch to get metrics. Alternatively, you can send it to other destinations such as Kinesis Data Firehose to send it to S3 and other places so you can store events for deleted domains for archives.

Price per metric – You can view basic Amazon SES metrics in CloudWatch for free. However, when you collect metrics using event publishing, you create custom metrics in CloudWatch. Each unique combination of event type, dimension name, and dimension value creates a different custom metric in CloudWatch. When you use CloudWatch, you are charged for each custom metric you create. For this reason, you might want to avoid choosing dimensions that can take many different values. For example, unless you are very interested in tracking your email sending events by "From" domain, you might not want to define a dimension for the Amazon SES auto-tag ses:from-domain because it can take many different values. For more information, see CloudWatch Pricing.