Good Afternoon Nupur.
From within CA Service catalog, this is functionality that needs to be implemented frirst.
You could decide to add an idea for this in this same community.
Should the SC-Request be linked to an SDM-Ticket,
you could send an email to that SDM-Ticket, adding an 'SDM-log-comment'
which then in turn could get synchronized to the related SC-request as an SC-request-Note.
Kind regards, Louis.