Who proves himself to be a kind and faithful servant in book 20 of The Odyssey?
Several servants and people just loitering around the castle are referenced in Book 20. Eumaeus is the swineherd most often referenced specifically for his kindness and loyalty especially in more condensed translations like those put in 9th grade textbooks. In fact, he is the one who greet Odysseus the beggar so warmly regardless of the translation.
However, if you are reading a longer translation, you will likely be looking for the character of Philoitius. He is the cowherd who speaks to Odysseus (still disguised) with great respect and loyalty for his master and expresses his longing for Odysseus' return.
Eurycleia is a female servant who organizes the servants to prepare the meal to be shared by Telemachus and the new stranger.