Please list an application of the ken straight line linkage.

Answer 1

It's surprising that your teacher did not mention any application when the subject was being taught.
The linkage essentially converts rotational motion into a straight line movement. The rotational motion usually comes from a motor, and the straight line movement can be used for daily applications such as opening a door (e.g. on a bus or a train), windows, robot arms, etc.

Some very basic information can be found rapidly by googling "ken linkage".