1) Adroitness 2) Aptitude 3) Command 4) Dexterity 5) Expert skill or knowledge 6) Expertness 7) French word used in English 8) Know-how 9) Proficiency 10) Skill 11) Skillfulness 12) Technical skill Found on https://www.crosswordclues.com/clue/expertise
expert skill or knowledge; expertness; know-how: business expertise. · a written opinion by an expert, as concerning the authenticity or value of a work of art, manuscript, etc. Found on https://www.infoplease.com/dictionary/expertise