。
I'm not familiar with this part of the problem.
Literal
I [topic-は] problem [attributive-の] this part [contrastive-には] familiar-not.
詳しい ('detailed, well-versed, knowledgeable about') is an い-adjective taking its target with に. 詳しくない is the negative. The contrastive は inside (には) foregrounds this specific part — 'as for this part specifically, (I'm not familiar with it).'