Allocated Sinister Jewel Sockets are visible on the left edge of the character portrait in the centre of the passive skill tree.

Unique Jewels cannot be socketed in Sinister Jewel Sockets, and modifiers to the effect of Jewel Sockets do not apply to Sinister Jewel Sockets.

They are entirely disconnected from the rest of your passive skill tree - they are not considered to be within any radius of any other passive skill, and no passive skill is within any radius of a Sinister Jewel Socket. Multiple Sinister Jewel Sockets are also not within any radius of each other. Radius effects of Jewels will therefore have no effect when socketed in Sinister Sockets.