The mother of Christchurch baby Ihaka Stokes has been asked what exactly happened on the day he died.

The trial of Mikala Stokes’ former partner, 23-year-old Troy Taylor, is in its second day in the High Court at Christchurch.

He's alleged to have assaulted the 15-month-old on July 2, 2015 and murdered him the next day.

Ihaka was found unconscious at the couple's Truman Rd property in the Bryndwr area of the city and rushed to Christchurch Hospital where he soon died.

Defence council Phillip Shamy spoke of a police interview conducted three hours after the baby’s death.

He asked her why she answered the question of “did you harm your child” with an “I don’t know.”

She’s told Mr Shamy she can’t remember what happened the day her son died.