Learn Finnish: Kenelle sinä puhuisit rehellisesti? - To whom would you speak honestly?

Kenelle is the allative form of kuka (who), meaning "to whom". We use the -lle ending here because the action of speaking is being directed to someone.

We are learning about consonant gradation in the conditional. Why doesn't puhuisit change its consonants?

Consonant gradation only happens to words that have the letters K, P, or T in their stem. Because the verb puhua (to speak) lacks these letters, its stem stays exactly the same when you add the conditional marker -isi- and the personal ending -t.

Can I leave out the word sinä in this sentence?

Yes, you can! The verb puhuisit already ends with -t, which clearly tells us that the subject is "you". Saying Kenelle puhuisit rehellisesti? is perfectly natural and very common.

How do we build the word rehellisesti (honestly)?

It is built from the adjective rehellinen (honest). To turn this type of adjective into an adverb (like adding "-ly" in English), you take its stem rehellise- and attach the Finnish adverb ending -sti.