Salaried person starting part time business of real estate agent, gst threshold limit for gst reg.?

No. Dealers earning Commission brokerage etc. need to be mandatorily registered under GST without thrash-hold limit.

Sir no benefit of Circular No. 57/31/2018-GST ?

where the example is given with regard to such person who are not an agent for supply of goods of Schedule I

and in my query the person is similar to example 1 & 2 of the circular. The Sale of Flat is between Builder and the buyer and this person in question has nothing to do with sale agreement or invoice.. he will get brokerage.
is this circular withdrawn or superseded by any other circular? Kindly help with it...

Thank you

Section 2(6) defines aggregate Turnover which includes exempt supply. Exempt supply - 2(47) in my understanding excludes supplies set out in Sch II. Schedule III (1) considers supply b/n employees to the employer not a supply of either service or goods. Section 24 ((1) (vii) specifies that those who make taxable supplies on behalf of the taxable persons are liable to be mandatorily regd. 

In this case the employee who provides some marketing services and earns a commission cannot be said to be providing the supply on behalf of another taxable person. he is providing services to that person. 

Therefore if salary income is 24 L and commission income is less than 20 lakhs, there is no need of registration unless he is liable to pay GST under section 9 (3) under Reverse charge mechanism.