Question

change the degree of comparison without changing the meaning if the sentence is in positive degree then please tell me the superlative and comparative degree(My brother is strongest man in the world )

Answer 1

it is in superlative degree.
positive:No other man in the world is as strong as my brother.
comparative :My brother is stronger than the other other men in the world.

Answer 2

The given sentence is:

My brother is the strongest man in the world.

I think you typed the question wrong . There will be 'the' after is.

This is in superlative degree.

Positive degree

No other man in the World is as strong as my brother

Comparative degree

My brother is stronger than any other man in the World.

Hope it helps you:-)