Where does the measurement begin if you have finger grooves and a choil without a guard ?
The measurement begins from where the blade would measured from if it had a guard, i.e., from right in front of the handle scales. Look at a Becker BK2 or BKanything that has handles. There is no guard so you start from the front of the handles. If there are no handles, scales or bolster to judge by, the general consensus is that measurement would begin behind a sharpening choil but in front of the "normal" gripping location.
Take a look at the Becker BK11 neck knife as an example. No guard, no bolster, no handles (unless modified by the owner). For this knife, measurement would be the longest straight line distance from the tip of the knife to a line running perpendicularly to that line as lined up on the the aft most edge of the blade area, which would be right at the sharpening choil. The edge grind is slightly angled aft, so measurement would go to the aft most point of the blade. The "handle" has a small "guard" stamped out with the whole blank, so that "could" be considered a guard of a sort. That would make the 2 options, "front of the guard" or "where a guard would go" the same point.
If there is a bolster or faint guard, is it the beginning of the measured blade?
I'm not sure what you mean by "faint guard", but any guard is a guard. Measurement begins at the front edge of the guard.
If you have a harpoon styled knife with a clearly defined guard at the beginning to the sharpened edge
does it matter how long the handle / grip is?
Handle length is not considered in blade measurement. The blade is the blade. The handle is not part of the blade.
Now, depending on how long the handle is MIGHT influence a LEO, Judge, DA, Jury on whether or not the instrument in question is a long handled knife or is instead considered to be a short bladed spear or sword.
Most states have laws that make it illegal to carry either a spear or sword in public. Some exceptions to that generalization, CA and AZ spring to mind with that regard, maybe VT or NH as well, but then local ordinances could come into play even in those states.
