If you wear suits frequently, you may have a stock of pocket squares and ties. Incorporating a classic pocket square into your outfit is an easy way to make an impression.
Yes, it is okay to wear a pocket square without a tie. However, this is not something that you should do without some consideration.
Yes, there are some job interviews where it is appropriate to wear a pocket square. However, some interviewers may not like the idea of the pocket square or find them to be too formal.
It's a good idea to have at least one black tie in your closet because black is one of the most versatile tie colors. It is appropriate for just about any event, from weddings to business meetings, and it can be worn with anything.