Have I to use here going to or will?

If I can not become both professions, I will do a high level law study or I am going to do a law study.

If I can not become both professions, I am going to do a law study.

Explanation:

Both will and going to are used to express the future.

Will is used when we are talking about decisions made right in the time of speaking, to make predictions about the present moment, to make offers, promises, threats and so on.

Going to is used for talking about decisions that are made before the time of speaking, then for making predictions about the future that are based on the current situation or moment.

In this example, the person talks about future plans that are already made, so it is the most suitable to use going to.