No, Mass Cure Wounds does not require line of sight in D&D 5e. When you cast it, you choose a point within 60 ft. of you, and the spell’s 30-foot-radius sphere emerges from it. However, as per the regular rules of spellcasting, you need to have a clear path to your chosen point. You do not need to see it, but nothing must be blocking you to the point, like a wall.