Friend with bpd said. I cant 
Ask how they are doing
Ask how their day was
Another redditor said to try asking "what" questions instead (what happened today? what interesting thing happened at work? Etc) 

But he turned them down and told me not to immediately. He got distant and said he is mentally and emotionally at his limits. I asked what to do, some redditors said to just be there show that i care, but i dont know how