There are several ways to quickly see a person's largest contribution.
In the supporter's page in the constituents area, go to the Contribution History tab. At the top, there will always be a contribution summary section. There is an area for Largest here like this:
If you wanted to see people's largest in a big list, you can also include this field in the export.
Once you have searched and generated your list, proceed to Take Action area.
Select 'Download', and then check the box for 'Contrib History', like this:
This will automatically include the details (amount and date) every person's largest donation in the resulting csv file.
Note: In addition to Largest, including this Contrib History will also include each person's LifeTotal and details on their Last contribution.