Is there a report to show how many emails are sent to each person?

The standard reporting options within Marketo are very simple and don't offer too much flexibility in terms of this. 

For clarity, are you looking for a total count (e.g. Email1: 3 emails; Email 2: 5 emails) or the names etc (Email 1: Newsletter, Webinar Registration, Webinar Reminder; Email 2 : Newsletter...)?

If you're looking for a total count, you could create a webhook that "counts" every time an email is sent and adds this value into a field within Marketo. This field could be wiped out each week, and values added to a Historical field so you can track previous weeks/months etc.

If you're wanting to identify the names of emails a lead has been sent, you could create a field within Marketo (e.g. Email Historical) that a Smart Campaign adds a value to every time an email is sent. That value could be the date and name of the email the lead has received. You could then create a Smart List of everybody who has had the "Email Historical" field updated in the past X days to see what has been run.

It's not simple, but these are the most straightforward options I could come up with.

If you don't have RCE, you'll need to create custom fields to track email names or counter fields to track number of emails sent - as suggested by Josh.

If you have RCE you can get such reports:

Count of Sent:

By email name:

We've got something similar in our instance. It involved creating a new custom score field called 'Email Count'. A listener campaign was set up whereby if an email is delivered, add +1 to the count. Then, wait 7 days until 11pm, and minus 1 from the count. That way, at any given time you have a clear idea of the number of emails sent to that person in the last 7 days.