For your friend GST number is required only if his turnover from that rent exceeds ₹40 lakh during a year and with regard to you since you are going to rent the shop under your own PAN registered with GST you don't need seperate GST number for this rent income you only need to add the HSN code of this income in your GST registration and you can easily show this rent income along with your other income in GST return.
If you need any help in filing ITR or GST return do let me know.
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