Composition have to pay GST on commission

Composition dealer receiving what...rent or commission ?

On rent

Rent income is from residential property (House, flat) or commercial property (shop , factory ect) ??
If received for commercial property , than its taxable.

If he received commission in real-estate

Income of Commission in real estate is also liable for GST, it's taxable.

How much % have to pay

You are required to pay 1% But..... kindly make sure that as per Section 10 of CGST , the Composition dealer can make supply of Services upto 10% of Turnover or 5lac in year whichever is higher.
So if your commission income is beyond 5 Lac then you cannot continue with it, need to opt for reqular scheme