The samāsānta affix is not applied to a word preceded by kim in the sense of reproach.,
Thus किं + राजन् = किंराजन् as किंराजा यो न रक्षति \He is no-king who does not protect\. किंसखा योऽभिद्रुह्यति, किंगौर्यो न वहति ॥ 5.4.91, 5.4.92, (II. I. 64). The compounding here takes place by Rule (II. I. 64).
Why do we say \when meaning reproach\? Observe कस्य राजा = किंराज, किंसखः, किंगवः ॥,