in your codex, for each planet you have a "codex entries found" bar that fills up as you find stuff. You can expand the list to get the details by clicking on the magnifying glass. It will have several sub-bars, one of which is the number of datacrons on the planet.:
I have been playing since pre-launch and had no idea about this.
I know there is a seperate category for datacrons, but it only lists them by number and not what stat they increased. This is also where the lore entry is located, since each datacron also holds game lore.