To recover data from the pendrive first try Recuva. That should be the easiest to use. Recuva - Undelete, Unerase, File and Disk Recovery - Free Download
If it does not help, you may try PhotoRec in Test Disk which is a powerful tool but requires a bit of learning curve. TestDisk - CGSecurity
Both the above do not write anything to the drive being recovered and absolutely safe to try.
For PhotoRec you may refer to the guide here
apart from the documentation in the Test Disk site.
To be specific to your problem the following screenshots should help. (provided PhotoRec can catch your pen drive
Then there are other programs like Minitool Partition Recovery and EaseUs Partition Recovery but the free versions will most probably recover only 1GB of data. Recover ntfs hard drive with MiniTool Partition Recovery. Free Partition Recovery Software - Recover Deleted FAT/NTFS/HFS/HFS+/HFSX/Ext2/Ext3 Partition in Windows and Mac OSX.
I shall leave it to other experts here in case Recuva and PhotoRec fail to bring results in your case.