penetrable

Capable of being penetrated, entered, or pierced.

On the east the high mountain-chain of Zagros, penetrable only in one or two places, forms a barrier of the most marked character, and is beyond a doubt the natural limit for which we are looking.

Capable of being fully understood.

A Boer may know you, but it will take you some time to know him, and when a certain stage in your acquaintance is reached, you may begin to wonder whether his real nature is penetrable at all.

A capacity is cognitively penetrable in this sense if that capacity is affected by the subject's knowledge or ignorance of the domain.