This is a single-arm, multi-cohort, multicenter, phase Ib/IIa clinical study designed to evaluate the safety and efficacy of Zeprumetostat (an EZH2 inhibitor) in combination with different therapeutic agents/regimens - specifically, the JAK1 inhibitor golidocitinib and the GemOx chemotherapy regimen (gemcitabine plus oxaliplatin) - in patients with relapsed or refractory peripheral T-cell lymphoma, not otherwise specified (PTCL-NOS) and T-follicular helper cell lymphoma (TFHL). The trial comprises a phase Ib dose-escalation phase and a phase IIa dose-expansion phase. Two combination cohorts are established: Cohort A (zemitostatin + golidocitinib) and Cohort B (zemitostatin + GemOx). Subjects will be randomly assigned to either Cohort A or Cohort B.