To ask someone ‘How was your day?’ in Spanish, you would say, ‘¿Cómo fue tu día?’
This phrase is commonly used in casual conversations to inquire about someone’s day. The word ‘cómo’ means ‘how,’ ‘fue’ is the past tense of ‘to be,’ and ‘tu día’ means ‘your day.’ So, the structure reflects what you want to know: the quality of their day in the past.
If you want to address someone formally, you can say, ‘¿Cómo fue su día?’ where ‘su’ is the formal version of ‘your.’ This is appropriate when speaking to someone you don’t know very well or wish to show respect.