Question

Why gratanio asks blessings of bassanio and Portia for his marriage?

Answer 1

so that just like bassanio chose a right casket and proved his love to be true...just like this....gratiano can also prove his love with nerissa to be true....and just like bassanio and portia...he can also make a strong bond with his beloved and love her forever....

Answer 2

Because he is the servant of bassanio and copied of them in marry