Efthokia’s name day is March 1, the feast of Eudokia.
Churches that follow the Old (Julian) Calendar keep the same feast on March 14 of the civil calendar. See everything commemorated on March 1.
The saint behind the name

Eudokia
March 1, Holy Woman, Ευδοκία
St. Eudokia was a Samaritan of Heliopolis in Phoenicia who lived in the early centuries of the Church. Wealthy and famed for her beauty, she was moved to repentance by the words of a monk named Germanos, was baptized, gave her riches to the poor, and entered the monastic life, excelling in fasting and prayer.
Also celebrating on March 1
These names share the feast, many of them other forms of the same name:
Eudokia, Eudocia, Docia, Evdokia
What to say on a name day
The Greek wish is Χρόνια Πολλά (Chronia Polla), “many years.” A call or a short message on the day is what people remember. See name day wishes you can send and what a name day is.