where can i add donation amounts if i choose /cart route

Those blocks are not yet created/adapted for the /cart route. Your users can choose a donation amount in the donation step of checkout though with the /cart route setup

Thank you for the reply .I have added donation step in checkout with the /cart route setup with multistep_donate checkout.
But i cant see the same donation step in checkout page.

and also is there any screenshot how this donation step will look like in /cart route? and where can i configure this donation step?

That is configurable in the settings of the field widget for the donation order item's amount field, and will display suggested amounts to donors in the donation step of checkout.