Where is the best place to practice parrying?
Solution 1:
Use the Cardinal Tower Bonfire as starting point. From there you have quick access to a lot of different Hollow mobs. These mobs have a variety of weapons, and attack with different speeds, and are great to practice parrying.
Additionally, they do not hit very hard. All in all, it is a area where you can easily control the settings and the pulls. If you blow out the wall, you'll have even more mobs to choose from very quickly.