Born in Krško,[3] Sokler started his playing career at the age of six, at the football school Nogobikci, before joining the youth sector of his hometown club Krško.[2] He came through the club's youth ranks, as he won the under-13 and under-15 national championship in 2012 and 2014, respectively.[2]
Having been promoted to the senior squad in 2016, aged 17,[2] Sokler made his Slovenian PrvaLiga debut on 26 November 2016, in a 4–0 defeat against Maribor.[4]
After two seasons at Celje,[6] Sokler joined fellow Slovenian top-tier club Radomlje on a permanent deal in July 2022.[3][9] He scored 10 goals in 31 games in his first season with Radomlje,[6] as they finished seventh in the league.[10]
In 2023, he claimed that he has often been mistaken for a woman, as Ester is actually a female given name in many countries, including Slovenia itself.[13] According to him, his parents likely chose to name him after Mi2's 1998 song "Moja teta Estera".[13]