You can now check Insights for your Google Posts. Here's how:
To view general insights for all your Google Posts, navigate to Posts - Insights - Google. You can select the timespan for your Insights.
To view Google Insights for a specific post, go to Posts. Select the Google post you are interested in, then navigate to the Insights tab
Impressions(clarification) - The number of times the post has been shown to a user
To view Google Insights for a single post on a specific location page, go to Posts. Select the Google post you are interested in. Navigate to published status type, select the page you're interested in, then click Insights: