@Padonak the simpilist answer is that it depends.
In a civil case regarding discrimination the level of proof is the "preponderance of the evidence" The standard is met if the proposition is more likely to be true than not true. The standard is satisfied if there is greater than fifty percent chance that the proposition is true. The evidence does not need to be as strong as in criminal case with beyond a reasonable doubt. In any case these are still very vague answers.
The severity of the act, pervasiveness, harm it causes all impact the situation.
As I have kind of learned that even with a smoking gun it can be very challenging. Employment law is very complicated.
First thing if there is discrimination going on the first thing is making hr/management aware and follow up with them to make sure they do something with it. You will want to find a way to document this. Email, Journal, Memo, recorded phone call (be aware of your state laws regarding recording others, my state requires all recorded parties to know they are being recorded.)
Depending on the type of discrimination if nothing is done and maybe you want to give them another chance go back to management/hr again.
You will want to document this as best you can. When I was tracking stuff I sent myself emails with the details like who, where, what, when etc. Then it had a date stamp.
If your company has a formal grievance policy you may need to work through that first. Actually you probably want to start there and see what policies related to discrimination are in place.
At this point there are many directions you can go. This is probably the point where you may want to at a minimum have a consultation with a lawyer. They can better inform you of local requirements or ways to still handle it at the company level. Sometimes a strongly worded letter from a lawyer can make a big difference.
Then you could go to your state or federal level and file a complaint. Some smaller municipalities have Equal Opportunity offices you can make complaints too. Also, if you belong to a union.
Usually you have to exhaust all of your efforts with the state and federal eeoc before you can file any kind of lawsuit.
I am not sure if the ACLU or some other organization may be able to assist either.