/data/data/com.lge.qmemoplus/databases/qmemoplus.db
For a bit of context, I "backed up" my LG QuickMemos from the "storage/emulated/0/Android/data/com.lge.qmemoplus" folder (friendly reminder to backup your LG phone with the official LG Bridge app), and started to delete some fairly important notes - or at least, notes that were important - since I had full faith in the back-up safekeeping any residue important information (so much so, in fact, that I cleared my clip tray, and emptied out the inbuilt QuickMemo trash).
Well, it turned out that the folder at "storage/emulated/0/Android/data/com.lge.qmemoplus" only contains the following: "Audios, Drawings, Images and Videos" - not the memos itself. And so, with a little bit of digging around the root directory, the actual path of the QuickMemo memo database was found.
Note that you may need root to access this folder (where rooting a LG phone is trivial).
Edit (October 2016)
Root is required to easily access the database file at the specified path.
So either chmod as root (to open the quickmemo database files for use without later root),
su cp /data/data/com.lge.qmemoplus/databases/qmemoplus.db /storage/emulated/0
An alternative method could be through recovering the LG (G4) Quickmemo+ file from a real backup, although it appears that the backup encrypts, or otherwise hides the database file.