Safia S, 16, is charged with "attempted murder, grievous bodily harm and support for a foreign terrorist organisation", a crime which carries up to 10 years in jail.
"The federal prosecutor has asked for a youth penalty of six years' imprisonment for 16-year-old Safia S," said the court in the northern city of Celle, where hearings are being held under closed doors as the accused is a minor.
Prosecutors said the German-Moroccan national, who is believed to have been radicalised as a young girl, had sought to catch the attention of police officers by following them at the main train station in the northern city of Hanover.
Prosecutors say the teenage girl was "motivated by members of the Islamic State group in Syria to commit this act" on February 26 last year.
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Meanwhile, they are seeking three years' imprisonment for 20-year-old Mohamad Hasan K., who is also on trial for failing to report Safia's plans to police.
The defence is expected to enter its plea on Friday, with a verdict scheduled for next Thursday (January 26), the court added.
The suspect Anis Amri, who was shot dead days later by Italian police, had sworn allegiance to the IS group.
Two attacks last July were also claimed by IS -- an axe rampage on a train in Wuerzburg that injured five, and a suicide bombing in Ansbach in which 15 people were hurt.
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