Depicts a mouth (口) interrogating a captured prisoner of war (卂). 卂 also represents the sound. The 口 (mouth) component was later reanalyzed as 言 (speech).
Shuowen Jiezi
《說文》：“訊，問也。从言，卂聲。，古文訊从卥。”
Components
言(iconic) — Originally 口 (mouth). Later reanalyzed as 言 (speech).
卂(sound, iconic) — Depicts a captive prisoner with their hands tied behind their back.