Alexius
Affiliated Quest: Sit in Judgment
Inquisition Perk: A Magister in Disgrace (Secrets)
If you took Alexius alive following the events at Redcliffe Castle, you can judge him at Skyhold. Sentence him to research magic for the Inquisition.
Servis
Affiliated Quest: Sit in Judgment
Inquisition Perk: Servis (Secrets)
After confronting Servis in the Western Approach, return to Skyhold to judge him. Servis can be conscripted as an informant, supplying useful information to Leliana.
Florianne
Affiliated Quest: Sit in Judgment
Inquisition Perk: The Noble Cadaver (Connections)
If Florianne was killed at Halamshiral, you have the opportunity to judge her remains at Skyhold. Sentence her remains to community service to give Josephine another agent.