在退役一年后,李宁开始了新的事业--成为一名商人。after his retirement 是介词短语,作为 a year 的后置定语,A year after his retirement,作为句子的时间状语;Li Ning ,名词,作为句子的主语;began ,动词,做谓语;a new career 名词,做began的宾语;as a businessman名词,补充说明 new career。
“A year after his retierment” 是时间状语,可以放在句首也可以放在句尾;Li Ning 主语;began 谓语; a new career 宾语; as a businessman 宾语补足语。