A sentence using "commendable" is, "John did a commendable job on his homework and received an A+." While "commendable" comes from 14th-century French and means "worthy of praise," it is often used to note that an action was positive. Someone might say, "Alex gave a commendable singing performance."
In some cases, a manager may use "commendable" to set up constructive criticism of an employee. The manager might say, for instance, "The effort that you put into this project is definitely commendable; however, the results fall short of the established goals." "Commendable" is also used to denote an unnecessary or gracious action, such as, "Helping me with the boxes was commendable."