Can I read in Japanese 臨機応変 / rinkiouhen- adaptability to all / like ‘ rinkioken’?
Can I read in Japanese 臨機応変 / rinkiouhen- adaptability to all / like ‘ rinkioken’, or there must be another character ‘ken’, which I still don’t know?

Question

Answer

No you can not. 
it is "rinkiouhen". 
臨機応変 would be used as an adjective which means "flexible" or "changable". 
e.g. 臨機応変な対応(rinkiouhen na taiou) = a flexible correspondence 

I have never heard "rinkiouken".

Answer

this words is ”rinki-o-hen”.
Its means"Addressed by changing the situation,"

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