As an aspiring comic in Los Angeles, Jo Koy often could only go on stage during ethnic theme nights. How he went from there to being a Netflix darling is part of the career journey the 49-year-old has penned in his new memoir. “Mixed Plate: Chronicles of an All-American Combo,” out Tuesday, is an ideal companion to Koy’s stand-up with its humorous — and at times painful — origin stories behind some of his most popular bits. The book shows how Koy’s half-white-half-Filipino background ultimately shaped his brand of comedy and his determination not to give up.