वो विधूनने जुक्

Operational rule vidhi

वा gets the augment जुक् (ज्) before the affix णि when the Causative has the sense of 'shaking'.

Word by word (padaccheda)

Target वः ṣaṣṭhī · ekavacanaRight context विधूनने saptamī · ekavacanaSubstitute / term जुक् prathamā · ekavacana

Target Ṣaṣṭhī (6th case): names what gets replaced, "in place of X" (1.1.49 षष्ठी स्थानेयोगा).
Right context Saptamī (7th case): "when X follows", the operation applies to what precedes (1.1.66 तस्मिन्निति निर्दिष्टे पूर्वस्य). Also a condition or domain ("in the sense of").
Substitute / term Prathamā (1st case): in operational rules, the substitute or the thing introduced; in definitions, the term or its referent.

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Full reading

वः विधूनने जुक्

Pāṇini leaves out words that carry over from earlier sūtras. Expand to see the rule as a reader actually understands it.

As a rewrite rule (sketch from case endings)

वः → जुक् / विधूनने

Replace vaḥ with juk when vidhūnane follows. Inherited words (anuvṛtti) may add further conditions.

Commentary

वा gets the augment जुक् (ज्) before the affix णि when the Causative has the sense of 'shaking'.
As पक्षेणोपवाजयति ॥ But आ वापयति केशान् when the sense is not that of shaking. This form could have been obtained from the root वज् 'to move", (Bhuadi 271) with the affix णि in the ordinary way without any augment. The special augment ज् to वा indicates that this root will not take युक्, which it would have otherwise done by the last sutra. The root वा belongs to Bhuadi 969(ओवै शोषणे) ॥

Śrīśa Chandra Vasu, The Ashtadhyayi of Panini (1897), via ashtadhyayi.com.