Hi Cruz.
You need 3 parts : the email engine configuration, a Scheduler to trigger it daily, and the subscription that will be called to prepare the email.
Part #1 : engine configuration. As Pehowe mentioned, there's an extension you can attach to Thingworx to help you with it. Even better news : RTPPM comes with one, so it should already be installed. However you may need to finish configuring it. See this link for more info on how to configure it. Notably, you will have to configure Thing PTC.FSU.CORE.Notification.Notification_TG which has the SendMessage service on it.
Part #2 : Scheduler. This should be simple, in Composer you can create a new Timer or Scheduler to trigger daily at the time you select. A Scheduler is probably better than a Timer for you in this case. Then on that new Scheduler, you can create the subscription that will listen to Me -> ScheduledEvent. The code will go there.
Part #3 : subscription. In the subscription, you will need to get the results of the KPIs and then call the SendMessage service. For the KPIs, you can look at HK's answer below, he's calling the KPI Report in a service. Then you would need to get the results into a text. And you should be able to send emails with this piece of code :
Things["PTC.FSU.CORE.Notification.Notification_TG"].SendMessage
({
"from": "someone@something.com",
"to": "someone@something.com",
"cc": "",
"bcc": "",
"subject": "Daily KPI report",
"body": "Put the results here"
});