My guess is that merely telling truth might work, as the suggestion could nudge the NPC into Bond Villain mode:
"these people are no threat, so I will reveal to them my great plan!"
"I can totally trust these people with this secret that I have been harbouring all these years!"
It does not ensure that the NPC will actually tell the truth, now. If, say, an innocent was Suggested that he reveal his plans when he actually has none, he might spin some up just to please the suggestion.
Your given wording, though, is not a good suggestion. A better one might be something like "You want to show us how dumb we are and reveal your real plans." Or "You absolutely trust me and will tell me everything you know." Your DM may actually like it, as it gives him a chance to roleplay a monologue.
No, twice over.
Believing something is not a course of action and suggestion is incapable of implanting beliefs. Suggestion can't suggest mental conditions or states, only activities.
Even if it could, everything that suggestion made someone do ends when the duration ends. For beliefs what that looks like would be kind of strange (wouldn't even a temporary belief continue to have effects on your mind?), which is fine, because suggestion can't induce beliefs.
So no part of this, including probably the actions, would work:
You feel that this item is ruining your soul. You will get rid of it, and you will go praying for 2 hours in order to purify your soul.
The first sentence won't work because it's not an activity. The subject would hear you say “You feel that this item is ruining your soul,” and would react just like anyone would who were just told how they feel — disbelief and mistrust.
The second sentence would probably not work, because someone with an awesome magic item would not find “get rid of it” to be reasonable, and someone who doesn't feel like their soul is in danger wouldn't find “go pray for two hours to purify your soul” reasonable.
If you want to pull off suggestions that rely on beliefs that the target doesn't already have, you have to do it the old-fashioned way: persuade them to believe something first.
Best Answer
A verbal component can be literally anything spoken in a specific manner, pitch or timbre, and varies based on the world you are playing in. Source: PHB pg. 203
Specific examples:
The Krynn play setting has verbal commands such as Shirak and Dumak to light and quench the light on Raistlin Majere's staff (the Staff of Magius). This can be shouted, spoken or whispered, as is evidenced many times throughout the War of the Lance and the Twins novels. These are single word spells that are quick and efficient for the effects. Later on in the novels, the more complex spells use more complicated forms of verbal components, an example of which can be found here:
http://dragonlancenexus.com/lexicon/index.php?title=Magius_Language
Forgotten Realms utilizes a rythmic chanting that can also be shouted, spoken or whispered as is evidenced by numerous books highlighting different kinds of spell casting in action. Drow elves muttering quietly while casting fireball is simply one example of such action. Priests and Clerics mouthing the words while whispering the phrases necessary to incite healing is another.
Since 5e doesn't actually give specific spell chants or state specific chants that are required, it's really between the player and the DM.
The bottom line is, a verbal component only requires that somebody make some sort of verbal incantation to use it. That can be a single word, a syllable spoken in a specific manner, or an entire string of magical sounding casting. So a caster could hide the verbal component in a simple introduction as a title to his name.
For this example I'll put the spell word in italics. Something like: "Hi, I'm Creston Driak Nullfire, blade for hire. Do you think your friends could help us out?"