What are some kavanos should one have in mind when sharpening a challa knife on Erev Shabbos? I'm sure I heard that there are kavanos but never learned what they are.
I once heard someone ask Rabbi Shlomo Halberstam Zatzal of Bobov - what Kavanos one should have when he puts on his Tallis? He responded the main Kavana one should have is that he is not hitting the person beside him with the Tzitzis when he is wrapping himself in the Talis. Based on this I would say the Kavana one should have is not to hurt anyone nearby, including himself when he sharpens the knife.
The custom to sharpen one's knife on Erev Shabbos comes from the Kolbo (Siman 31) and Sefer Chayei Olam from Rabbeynu Yona (Siman 309) and is quoted by the Beis Yosef (OC 250 "V'yashkim") and Rama (250:1). The Rama explains that it is considered honoring Shabbos to prepare for the meal, and the Mishna Berura (S"K 5 based on Rokeach) adds that if the knife is blunt and does not cut well it could G-d forbid lead to fights in the house.
The Kolbo writes that it the Sifri derives this from the verse (Iyov 5:24) "You shall know that peace be in your tents" [although it is not in our copies of Sifri], and the Chayeh Olam learns it from the verse (Shemos 16:5) "They shall prepare that ("es") which they bring in". The word "es" is similar to (Yeshayahu 2:4) "le'itim ve'limazmeros" - "plowshares and pruning hooks"; since they are sharp instruments similar to knifes we derive the obligation to prepare the knifes on Erev Shabbos.
The Sefer Korban Shabbos (Perek 1 Siman 7) explains the Kabbalistical meaning behind sharpening knives on Erev Shabbos. Shabbos corresponds to the seventh millenium where evil will be banished from the world, and the food we eat on Shabbos symbolizes the Divine revelation we will then receive. Food cut with a blemished knife is a source for evil (as it creates ne'vaila), and therefore on Shabbos when evil has no power it is not fitting to eat from such a knife.
Based on the above, I would suppose that the simple kavana should be to get ready for Shabbos and to avoid strife in the house, and a more Kabbalistic kavana that the forces of Shabbos will be banished on Shabbos.