知

Left 矢 - the arrow radical, indexing radical for 知. Pictures a feathered arrow with shaft and barb. Anchors 知 in a tight family of arrow-related characters: 短 (short - shorter than an arrow), 矮 (low/short), 矩 (carpenter's square). The arrow image is key to the meaning: knowledge flies straight to its target like an arrow.

Right 口 - the mouth, here the speaking mouth. The compound picture is famous: words from the mouth (口) that fly as straight and fast as an arrow (矢). To know something is to be able to speak it instantly and accurately, without hesitation - 知 is knowledge tested by speech. Pure ideographic compound, no phonetic role.