somewhere是副词,意思是“在某处,到某处”在句子作状语,或者是名词“某处”,在句子中作宾语。some place中,place是名词,some是代词,修饰名词place,作定语。some place意思是“某个地方”,在句子中作主语或宾语,例如:

I know it's here somewhere. 我肯定它在这儿某个地方(摘自《牛津词典》)(somewhere作状语)

I needed somewhere to live. 我需要某个住的地方(摘自《柯林斯英汉双解大词典》)(somewhere作宾语)

He had gone to some place in Africa. 他去了非洲的某个地方(some place作宾语)