Where can I find the autocorrect / user dictionary on the iPhone and how can I have a look into it?
You can view the files in iTunes backups of your iPhone using iBackupBot. Open the software, choose your Backup, then sorted by Path find Library/Keyboard/dynamic-text.dat.

It's not possible to view the user dictionary directly from the device without jailbreaking. Jailbreaking does not delete the dictionary.