re pmessage number 18
I, too, was missing the search box but nothing in the previous replies helped. Then Googled "lost cortana box" and got to howtogeek.com's discussion of how to hide the search box (the opposite question). The answer: right-click on any empty space in the taskbar, click on Cortana, and either click on "hidden" to hide it or on "show cortana icon" to show just the icon or "show search box" to do that.
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OK on my W10 just upgraded to the latest Fast Ring build 14367 I had no Seach box but on the task bar whilst not an actual Cortana icon on the left was a tempting plan white circle. mousing over it revealed Cortana's catch phrase "Ask me anything" so I right clicked it and saw a useful option to "show touch keyboard button" which I unchecked as it had tended to get in my way anyway.I then thankfully found that simply clicking the circle showed the Cortana details and the good old searchbox which was sorely missing
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