The personal dictionary is the property of the keyboard app, and therefore different keyboards will store it in different places. Most likely it's part of the keyboard app's internal data, so will be in /data/data/com.samsung.whatever-they-call-their-keyboard-app, which you won't be able to access without root.
However, most keyboards do allow ways of editing it. A few might provide access to it via the keyboard's settings, but it's more common these days for them to let you edit predictions by long pressing the predicted word and telling it to remove that one from the dictionary, with adding new words being done automatically as the keyboard learns from your typing.
If the built in keyboard doesn't suit you the simple answer is to install a different one.