Incomes not covered under gst

Cash Deposits exceeds Rs. 20 lacs in 2017-18 in the current bank account. The assessee is actually doing taxable business but hasn't taken GST no.? 

What incomes are not covered under GST? For what business, receipts exceeding Rs. 20 lacs, GST is not required? What business we can show in his Income Tax Return, so that it doesn't call for any query from the ITD?