I'm not sure what you mean but I'll just reiterate the requirements mentioned on the wiki here: https://wiki.housamo.xyz/Character_Quest
In order to unlock the character quests,
1. You have to own the card (any version).
2. You have to have limit broken them once. This involves leveling them to the level cap (30/35/40) and then using the necessary god shards/crystals. This can be done by choosing the third option of the team builder menu as shown here: https://wiki.housamo.xyz/Menu#Team_Builder
3. You need to have done the necessary story quest. For example, to unlock Shirou's character quest, you need to have completed chapter 2 (all the story quests in Shinjyuku).
Currently there are only character quests for six characters, Shirou, Oniwaka, Bathym, Claude, Magan, and Garmr. Other character quests are planned to be released in the future.
For each of these characters, there is only one character quest at the moment. From the endings of the quests, it seems like they might implement more character quests in the future for the same character.
Location wise, they should appear generally where you encounter the character in the story quests. Since most of the characters currently receiving character quests are part of the Ikebukuro Berserkers, most of the character quests to be released are found in Toshima.
Concerning the second requirement, skill breaking is only possible if you have the necessary god shards/crystals and money. In order to obtain these items more easily, the current event quests distribute these items/money.
The introduction of being able to play past events is a way for people to play the character quests of event characters such as Jedd when the quests are eventually implemented. This is a way to fulfill the third requirement mentioned of having to play the story quest of that character.
tl;dr: Fulfill the three requirements and look in Toshima/Shinjyuku. If you're asking about where the rest of the character quests are, they aren't implemented yet.