Yasunori leaned against the armrest, gazing with bewildered eyes at the breakfast laid out before him.
Literal
Yasunori [topic-は] armrest [to-に] body [object-を] entrusting, in-front [to-に] put-out breakfast [to-に] bewilderment [possessive-の] eyes [object-を] applying was.
脇息 (きょうそく) is a traditional Japanese armrest used when sitting on tatami — immediately signals a historical or traditional setting. 朝餉 (あさげ) is an archaic/literary word for breakfast (modern: 朝食/朝ごはん). 当惑の目を当てていた ('was directing eyes of bewilderment') is literary narration. The whole sentence paints a period-drama scene with specialized vocabulary.