The correct pronouns to complete the sentences are:
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"Will we met yesterday is going to groom our dogs." (This sentence is incorrect as "Will" suggests a future action; it should be "Will we meet tomorrow ...")
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"_ was he again? I don't remember meeting anyone."
The correct pronoun to use here is "Who." So the complete sentence would be "Who was he again? I don't remember meeting anyone."
So, the answer is Who for the second sentence.