No. But snow speaks finnish.
In this case is the puhu needed?
It works with and without it. When saying "Osaavatko karhut venäjää?", it can also mean that do they understand Russian even if they couldn't literally speak the language.
When do you use"puhu" and when do you use "puhua"
"puhua" is the infinitive you will find in dictionaries. You have to use it after "osata" or "haluta" for example (just like in English). "puhu" is another infinitive (if you can say it like that) which is used after the negation verb.
Onko tääs tätä punainen sienit ??