Your Patronus is determined by a series of questions you answer during the "Wand" and "Patronus" sections of the Pottermore Sorting Ceremony. These questions are designed to reveal your personality and your core values, which then inform the Patronus assigned to you.
So, while you can't directly get the Stag Patronus, you can try to answer the questions in a way that reflects the traits of a stag, such as:
* Loyalty: Do you prioritize your friends and family?
* Courage: Are you willing to stand up for what you believe in, even if it's difficult?
* Leadership: Do you naturally take charge and inspire others?
* Strength: Are you resilient and able to overcome challenges?
However, even answering in a way that aligns with these traits doesn't guarantee you'll get the Stag Patronus. It is ultimately determined by the Pottermore algorithm based on your answers.
If you're hoping for a specific Patronus, there's no way to cheat the system or force a certain outcome. Embrace the Patronus you're assigned and remember that it's a reflection of your unique personality, just like James Potter's stag represented his own qualities!