A recent blog post from Christopher Culver brings to my attention an apparent family of Turkic word roots showing irregular variation in form: *künäš ~ *qujaš ‘sun, day, heat’. Aside from the alternation *n ~ *j (for which *ń seems to be a standard explanation), these seem to make up a neat pair of front/back variants.
I am wondering however if this relationship might be illusory, and if there might be an old Uralic loanword in Turkic involved here instead. There are a few Uralic word roots (themselves probably in some sort of an obscured correlative relationship) that seem quite relevant here:
- *kaja ‘sun, to shine’ (> Finnic *kajasta- ‘to dawn, to shine’, Lule Sami guojijdit ‘to rise (of sun or moon)’, Samoyedic *kåjå ‘sun’, etc.)
- *kojə ‘dawn’ (> Finnic *koi ‘dawn’, Hungarian hajnal ‘dawn’, Mansi *kuj ‘dawn’, etc.)
Of particular interest is the Hungarian word, which seems to show the exact same “suffixal” elements as Turkic. This even has a formal equivalent in Khanty: *kuuńəɬ´ ‘dawn’ (apparently showing a change *jn > *ń, in neat parallel to the change *jt > *ć that was proposed by Aikio recently ), coming closer yet to the Proto-Turkic form.
It’s hard to say though what the dangling element -nal is here. It’s neither an independent word root on its own, nor a regular derivational affix. If I had to speculate, a compound *kojə-n‿alŋV > *kojnal- ‘beginning of sun’ could be assembled… but this seems a bit contrived semantically. Also I am not convinced if Khanty *aaLəŋ ~ Mansi *aaɣəl ‘beginning, end, point’ is an inherited root at all. 
And while phonetically the Khanty form in particular seems like a prime loan original, the semantics are a bit off. Is the meaning ‘dawn’ in Hungarian and Khanty perhaps secondary, from earlier ‘sun’ or the like? Or was there instead a shift ‘dawn’ > ‘sun’ in some transmission language along the way?
Some Turkologists, I’m sure, could also see it as an obstacle that this etymology seemingly requires adhering to sigmatism (reconstructing a Proto-Turkic lateral” *l₂ that later shifts to *š in Common Turkic) over lambdaism (reconstructing PT *š that shifts later to *l in Oghur Turkic). Now, yes, from what evidence I’ve seen, I lean on the view that sigmatism is the better solution … But it is, however, not an entirely inescapable assuption here. Say we instead assumed that early Oghur maintaines *l₂ for some time apart from *l (perhaps indeed as a lateral fricative [ɬ]? ) Then we could posit an etymological sound substitution to have occurred during propagation to the other Turkic languages: Khanty *kuuńəɬ´ → Oghur #qujal₂ → Common Turkic *qujaš.
Independent loaning to different Turkic varieties might also be chronologically preferrable to assuming loaning already to unitary Proto-Turkic. Christopher notes that *qujaš seems to have a kind of northerly-leaning distribution across the Turkic languages… not bad news for an attempted Uralic loan etymology, I’m sure.
 Aikio, Ante (2014): Studies in Uralic etymology II: Finnic etymologies. Linguistica Uralica 50:1.
 There is, yes, a rather similar word root in Finnic: *alka- ‘to begin’ — but this does not quite correspond regularly to the Ob-Ugric words, esp. on account of the discrepancy between *ŋ and *k. The vowel correspondence Kh *aa ~ Ms *aa is not typical of inherited Uralic vocabulary either.
 But note that this does not compel me to take a stance on the similar rhotacism/zetacism debate, nor to consider *l₂ of “Altaic” inheritance.
 Which even brings to mind the East Uralic shift *š > *ɬ, rather similar to the shift *š > *l posited by the lambdaist side of the Turkic debate.