Take your most recent pirep from the DB. What is in the raw_data column?
If there is data there, you can get it working. Take a look at the exaple Chart.js charts and you'll see the format it requires. It should be a simple JS array format
data = [1,2,3,4] etc.
And then each element of the array should have an associated element in the labels array. But check the docs for this.
A quick solution would be to just generate a script that creates a properly formatted string, and call it inside the .tpl/.php file. I guess the better way would be to perform some sort of AJAX call to get the data then do a $.each() on the array.
Did this for a VA.
Take a look at the part of the code