جَلَسْتُ جَلْسَةَ الْقَارِي
Translation: I sat in the manner of a reader.
جَلَسْتُ: past verb with attached subject pronoun.
جَلْسَةَ: accusative absolute object in an iḍāfa; describes a manner of sitting.
الْقَارِي: genitive second term of iḍāfa, describing whose manner is meant.
Do not infer “one occasion” as the intended point here; the iḍāfa specifies the type of sitting.