Nightclubs in GTA Online are businesses included in the game as a part of the After Hours update. Any of the ten clubs can be purchased at the Maze Bank Foreclosures website.
To complete this daily objective, you need GTA$500. Call Brucie and select the only available option in the menu — “Bull Shark Testosterone”.
Right after that, a green capsule that marks your testosterone will appear on the map. Pick it up, and the daily objective will be completed.
You can also pick up some Bull Shark Testosterone in deathmatches or in any other mode where it appears.