There are two areas you can export two types of reports. One is the data feed report the other is the diagnostics report.
Export the data feed report
- Login to your Google Merchant Account
- Click on your data feed, which is located under Products > Feeds
- Than if you have any errors click on Download full report
Export Diagnostics report
- Login to your Google Merchant Account
- Click on Products > Diagnostics in the right hand side menu
- Click on Items inside current issues
- Click on the arrow on the right hand side (circled in red on the image below)