If you have concerns, it is okay to state them and ask directly about mental health and suicide.
In fact, asking shows the other person that we are willing to have the conversation, and it can actually provide comfort and increased possibility of honest communication.
Warning signs of suicide include talking about suicide, expressing hopelessness, seeing oneself as a burden to others, displaying severe/overwhelming pain or distress, and marked changes in behavior, emotionality, or goals. You do not have to see any of these though to feel concern and open up a conversation.
You do not have to understand it, but you also do not have to change it. Validation is accepting the person where they are at, and support is showing that you are right there with them. "I hear you," "I am here for you," "I love you" are all validating and supportive statements.
You do not have to have the answers, and you are not going to be able to fix it. But you can help to focus on immediate next steps - sitting for a few moments, getting a drink of water, calling a crisis line together, seeking out other supports...just focusing on one step at a time.
Finding out a loved one is suicidal is a crisis situation, and it can leave you feeling confused, scared, helpless, and powerless. Make sure to find your supports as well, and know that you never have to handle this alone.