Question:

A man purchased shares in a trading company. When the company started, a share cost $500. When the man purchased his share it cost $1000. Now the price is $500 per share. On what price will he pay zakat?

Answer: حامدا ومصليا ومسلما
He will pay zakat on the current price i.e. $500.
(See Fatawa Darul Uloom 6/146)
And Allah Ta’aalaa knows best
(Hazrat Mufti) Ahmed Khanpuri (May Allah preserve him)
Mahmoodul Fataawaa (2/41)