Alright, let me give another high-end giant main perspective on this.
Taunt: Effective especially at higher ranks, if you need to get aggro off a buddy, or bring the enemies to you. (Unless they're archers, then it just brings trouble.)
Training Taunt: Go into provocation and spam it. I'm serious. Those spikes have low CP, but there's a lot of them, so it can train taunt extremely easily.
Wind Guard: At a high rank, this skill can tank many attacks, including attacks that would trigger your Defense skill and make you susceptible to big damage intake.
Training Wind Guard: The middle room in Tara's Sulfur Spider mission where there are literally tons of those little spiders that attack really fast.
Training Wind Guard Part II: There's a requirement that makes you use melee attacks while using it. This is where Provocation comes into play. See video below.
Training Wind Guard Part III: There's another requirement that needs magic and archery attacks. Again, video below explains it all.
Stomp: I can somewhat agree with this, this skill is completely useless at low ranks, but it does give a lot of strength, including it's Master title. But, it can be useful for giving you a split second of air during a fight, because it stuns whatever it hits.
Training Stomp: Video below.
Mission: Tara's "Their Method".
Throwing Attack: I've seen high-end giants with Throwing attack, and even without Elemental reforges (fire, ice, lightning, etc) they can still hit up to 15,000 damage and higher. This is a skill that can be outclassed by a plethora of other skills, but in of itself, it's quite useful for one-on-one fights.
Training Throwing Attack: Again, the same way of training as stomp, just leave the finish rule as it is. This one is CP-dependant, so you'll have to hold the ALT key and see how strong the enemy is.