where do they manufacture their vehicles?
Most of them are produced in Japan at the Tahara plant in Aichi and Miyata plant in Fukuoka. Recently they have started plants in Ontario, Canada, Georgetown, US, and Bidadi, India.
Lexus
Through the 2000s (decade), most Lexus sedan and SUV production has occurred in Japan at the Tahara plant in Aichi and Miyata plant in Fukuoka. In addition to the Tahara factory, Lexus vehicles have been produced at the Miyata plant (Toyota Motor Kyushu, Inc.) in Miyawaka, Fukuoka, Higashi Fuji plant (Kanto Auto Works, Ltd.) in Susono, Shizuoka, and Sanage plant (Toyota Boshoku Corp.; Araco) in Toyota City, Aichi. Front-wheel drive cars, such as the ES and HS, are produced in the Fukuoka Prefecture. The Kokura plant in Kitakyushu, Fukuoka, which opened in 2008, is a dedicated hybrid production site for Lexus models such as the gasoline-electric RX. The North American–market RX 350 (since the 2004 model year) is produced at the Cambridge plant (Toyota Canada, Inc.) in the city of Cambridge, in Ontario, Canada, which is the first Lexus production site located outside Japan. In late 2015, Lexus started to assemble North American-spec ES 350 sedans at the Georgetown plant (TMMK, Inc.). In 
how does lexus ensure the high quality of every lexus vehicle By placing an emphasis on targeting specific vehicle development standards.
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Lexus [SEP] Assembly plants
The first Lexus vehicles were manufactured in Toyota's Tahara plant, a highly sophisticated, computerized manufacturing plant in Japan. Lexus production techniques include methods and standards of quality control that differ from Toyota models. At the Tahara plant, separate assembly lines were developed for Lexus vehicles, along with new molds and specialized manufacturing equipment. Welding processes, body panel fit tolerances, and paint quality requirements are more stringent. Lexus plant workers, typically veteran technicians, are identified via repeated performance evaluations and ranked according to skill grade, with limited applicants accepted. The highest level "takumi" (Japanese for "artisan") engineers are responsible for maintaining production standards at key points in the assembly process, such as testing engine performance.