I am trying to make a spell I am calling "Taboo" and would like a little input on Balance. As this is a non-damage dealing high-level spell its power is very subjective. 

You shatter the 9th circle of Divination to curse the name of a Person, Place, or Thing (must be a propper noun.) Once per day, when someone speaks aloud the Cursed Name , you magically learrn the name and location of the creature that spoke it.you can use your reaction to do one of the following. 

• Cast the Spell Scrying  on the creature whom spoke the name without requiring the target to fail a Wisdom Saving throw.
• Cast the Spell Teleport to the location of the creature whom spoke the name with a 100% success. 
• Cast the Spell Harm on the creature whom spoke the name without requiring the target to fail a Constitution Saving throw. 

If the creature who speaks the word is protected from Divination Magic such as in an AntiMagic Field the caster simply only knows the name was spoken, not where and by whom. 

This effect lasts until until dispelled. The spell ends early if the caster casts this spell again or if the caster dies. This spell cannot be dispelled except by the wish spell or divine intervention.

I'm trying to go for the BBEG, don't say lord Voldemort kind of thing... any ideas? too weak? too strong? 

Check out the chosen of mystra. Laeral Silverhand. She has a trait like this.

Otherwise add wisdom save, if the target fails you can contact her with sending spell and in addition cast scrying or teleport. You can use this reaction only once per day.  Otherwise you can speak, teleport or scry a whole nation. And make it 8th level.

As I see it, the caster is the one teleporting when a name is spoken, correct? If so, I believe wording should be added specifying that the caster must teleport to the creature that spoke the name.

I also think adding a 3rd option to cause damage to the speaker of the name would fit the flavor you're going for. Like people believe if you speak this name, they'll burst into flames (by taking 10d6 fire damage or something similar when they speak it)

One last thing, some spelling/phrasing corrections to help make the spell more readable:

• Change "Person, Place, or Thing (Must be a propper Noun)" to "person, place, or thing (must be a proper noun)". Only proper nouns need to be capitalized. So "You Shatter" should also become "You shatter". The 'y' is the first letter of the first word so that stays the same.
• Change "someone speaks allowed" to "someone speaks aloud"
• Remove the word simply from this sentence "the caster simply only knows the name was spoken, not where and by whom"
• for the final portion, instead of saying "this effect lasts until", change the duration of the spell to 'until dispelled' and write in the description "The spell ends early if the caster casts this spell again or if the caster dies.
  This spell cannot be dispelled except by the wish spell [or divine intervention]."

You can ignore the part in brackets if you use this template if you feel it doesn't match the idea you had. I hope these comments help with your spell!

Happy homebrewing!

I like the idea of other options. I'd have a more subtle one in there too, something like the speaker getting hit with a bane-like effect where they get a d4 penalty on all their ability checks, attacks and saves for the next 10 min or even the next hour. Basically an "inviting bad fortune onto yourself" sort of effect when the caster can't be bothered doing anything worse

I have updated the spell for further review. 

Quote from Cporter5 >>

If the creature who speaks the word is protected from Divination Magic such as in an AntiMagic Field the caster simply only knows the name was spoken, not where and by whom. 

 Based on this sentence, it's implied that the caster knows who spoke the name aloud. If so, there should be some text explaining this before the 'once per day' choices are shown.

Maybe: "You shatter the 9th circle of Divination to curse the name of a person, place, or thing (must be a proper noun). Until the spell ends, whenever the chosen name is spoken aloud, you know the name and location of the creature that spoke it. In addition, once per day, when a creature speaks the cursed name aloud you can use your reaction to do one of the following."

The intent might have also been to only have the caster know who spoke if they choose to cast scrying. But if that were the case, the quoted portion above doesn't need to be included.

Also a note on the teleportation portion. It might be better to simply say "You teleport to the location of the creature whom spoke the name" without actually casting the spell teleport. Casting the spell usually would mean that failure is possible, but since it isn't, the only things casting the spell adds are: 

• The caster can teleport with other creatures (which is unlikely to happen because they must use their reaction to do so)
• The teleportation can be countered with counterspell

Neither of these seem to be beneficial to the spell overall, so I would suggest replacing the casting of teleport with a teleportation effect that can't be countered and only allows the caster of Taboo to teleport.