As shown in the figure the corner of following shape need to be removed to make it dashed line. I am trying to use knife tool to cut the portion of the line. But failed to do so. Is there any possibility to cut the part of the line tool?
The knife tool won't work on an open path with a stroke. It only works on closed paths.
Example. The top line is an open path with a stroke. The bottom line is identical but has been Expanded to a closed path (outline) with a fill.
If you want a dashed line, it's probably easier to simply apply a dashed line to the stroke in the Strokes panel.