First you will have to enable the Application Generated audit in Windows, then you will need to enable the audit in ADFS. This is described here. And you will have to parse the events. The list of all events is available here.
But since you have Office 365, you have Azure AD and Azure AD Connect. There is a monitoring tool for ADFS called Azure AD Connect Health for ADFS. It's an agent you install on your ADFS servers (and WAP servers) and as long as the audit is configured properly in your farm, you get statistics from the Azure AD portal:
And it also alerts you in case of problem or configuration issues (like configuration putting your environment at risk). Have a look here. It requires Azure AD Premium licenses though.