Click on "Developer" in the left navigation to bring up the Integration Health page.

Scroll down to find the events you send, and any errors that need to be fixed.

You can expand any event to see what it contained.

 When you click on any bars in the graph overview page, it will take you to specific logs for that time period. 

You can also click on a user's id in blue to visit their page. On a user's page, You can click on their Activity section to see the events that were sent for them in particular.