The headings for the Google Sheet that the trips are posted to are as follows:
A. Vehicle Name
B. Trip Started (Date and Time)
C. Trip Ended (Date and Time)
D. Trip Distance in Miles
E. Trip Duration
F. Average MPG
G. Fuel Cost (USD)
H. Fuel Usage in Gallons
I. Number of Hard Brakes
J. Number of Hard Accelerations
K. Duration over 70 MPH
L. Duration over 75 MPH
M. Duration over 80 MPH
N. Trip-Path Image URL
O. Start Location Longitude
P. Start Location Latitude
Q. Start Location Map URL
R. End Location Longitude
S. End Location Latitude
T. End Location Map URL
You can locate this information in the IFTTT app by opening the applet and tapping on the icon in the upper right corner:

On the next screen you can change the setting of the applet and see what the headings are:

A. Vehicle Name
B. Trip Started (Date and Time)
C. Trip Ended (Date and Time)
D. Trip Distance in Miles
E. Trip Duration
F. Average MPG
G. Fuel Cost (USD)
H. Fuel Usage in Gallons
I. Number of Hard Brakes
J. Number of Hard Accelerations
K. Duration over 70 MPH
L. Duration over 75 MPH
M. Duration over 80 MPH
N. Trip-Path Image URL
O. Start Location Longitude
P. Start Location Latitude
Q. Start Location Map URL
R. End Location Longitude
S. End Location Latitude
T. End Location Map URL
You can locate this information in the IFTTT app by opening the applet and tapping on the icon in the upper right corner:

On the next screen you can change the setting of the applet and see what the headings are:
