Pure transliteration of English 'topology' - 拓扑 (tuò-pū) ≈ 'topo'. The 学 (xué) is then added for the academic field: 拓扑学. Note 拓 here is read tuò (not tà - tà means 'to make a rubbing of an inscription').
mistakes
拓 has two readings: tuò (to expand, develop - as here) and tà (to make a rubbing). For 拓扑 always use tuò; for 拓片 (ink rubbing) use tà.