Where do you find the location a liberty silver dollar was minted?

ALL silver dollars were "Liberty" dollars because they had a picture of Miss Liberty on them, so you have to know what style or date you have. Also, any dollars minted at Philadelphia will not have a mint mark, so a "plain" dollar coin is not an error.

Seated Liberty design: Beginning in 1846, on the reverse below the eagle. Possible mint marks are O, S, CC

Morgan design: 1878 to 1904 and 1921, on the reverse above the DO in DOLLAR. Mint marks are O, S, CC, and D; D only on 1921 issues.

Peace design: 1921-1935, on the reverse between the Word ONE and the tip of the eagle's tail.