Candy is sometimes countable. To use a few brand names, I consider small candies eaten by the handful, such as M&Ms or Skittles as candy. Larger pieces, individually wrapped and eaten one by one, are candies.
I usually talk about candy as in your example #1: Where is the candy? You give a bit of a problem in that you mention there are only a few pieces, and we might refer to that small number (easily countable) as candies, but since we are asking where they are (we can't see them and presumably we don't know how many there are), we would still say candy.
Yes, 'Where is the juice?' is fine.
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