1. Increase the damage dice for all natural weapons.
First let's address the Strong Jaw spell. It increases the damage rolls of each of your natural weapons. To address your secondary question, re-read the beginning of the spell's text:
Each natural attack that creature makes...
Fortunately the spell description contains a table that shows the new damage values for your natural weapons. The giant squid's normal size is Huge, and 2 sizes larger is Colossal. So the damage dice change as follows:
- 2d6 (bite) increases to 4d6.
- 1d6 (arms) has no match in the Huge column, so instead find any 1d6 and move two spaces right, which gives you 2d6.
- 4d6 (tentacles) is considered Colossal size on the chart, so you double it to 8d6. Since the giant squid uses tentacles for its constrict ability, you also increase the constrict damage dice.
2. Increase CMB and CMD by +1.
Next is the Powerful Shape feat. This effectively adds +1 to your CMB and CMD, but does not actually benefit your attack or damage rolls. For the giant squid, you add this bonus to your grapple check when using grab.
This also means you count as one size larger (Gargantuan) for the purpose of the grab ability, which you can now use against Gargantuan or smaller creatures!
Unless otherwise noted, grab can only be used against targets of a size equal to or smaller than the creature with this ability.
Note that the giant squid has the grab ability for its tentacles, which can be a secondary natural weapon. When you use Wild Shape, you don't gain the creature's feats, so you don't gain Multiattack. If you use tentacles as a secondary attack, the resulting grab check could still be at a -5 penalty.
Using the druid's BAB and the adjusted Strength modifier (STR), the offense statistics would be calculated based on which attacks or maneuvers you use. Note that these formulas may be adjusted by other miscellaneous bonuses or penalties.
When making primary natural attacks, or using a standard action to attack or initiate a grapple, you use the following:
- Attack roll = d20 + BAB + STR - 2 (size)
- Bite damage roll = 4d6 + STR
- Arms damage roll = 2d6 + STR
- Tentacles damage roll = 8d6 + STR
- Grapple maneuver = d20 + BAB + STR + 2 (size) + 4 (grab) + 1
- Other maneuvers = d20 + BAB + STR + 2 (size) + 1
- Constrict damage roll = 8d6 + \$\lfloor\$STR*3/2\$\rfloor\$
If you make a full attack, then your tentacles are a secondary natural weapon, and you use the following instead for your tentacles:
- Attack roll = d20 + BAB + STR - 2 (size) - 5
- Grab grapple check = d20 + BAB + STR + 2 (size) + 4 (grab) + 1 - 5
- Damage roll = 8d6 + \$\lfloor\$STR*1/2\$\rfloor\$