He is not sure about the matter.

他对此事毫无把握。

《新英汉大辞典》

He is not sure he wants to rejoin them.

他不想再加入到这些人中间。

youdao

A chastened Mr Kivuitu now says he is not sure Mr Kibaki won the election.

奇弗·伊图先生现在讲道，他也不确定奇贝吉是否赢得了选举。

youdao

The scientist says this mission has been planned for many years, but he is not sure when it will happen.

VOA: special.2010.05.25

But Cheney said he is not sure the Obama administration will do what is necessary to keep Iran from developing nuclear weapons.

VOA: standard.2010.02.14

Republican Congressman Jeff Flake said at the news conference he supports opening up to Cuba even though he is not sure how its government would react.

VOA: standard.2009.05.06

The president testified he is not sure if he knew the subpoena asked for gifts.

CNN

Mike McStay says he is not sure if the family is on the video.

CNN: Three years later, no sign of missing family

Meanwhile, Iron goalkeeper Joe Murphy has admitted he is not sure if he will still be at the club next season.

BBC: Scunthorpe manager Alan Knill prepared for League One