The Lalita Sahasranama Stotra belongs to the Uttarakhanda (latter part) of the Brahmanda Purana. In which chapter can I find the work??
As per this version of the Lalita Sahsranama Stotram hosted by the Kamakoti.org, the Stotram is present in the 2nd chapter of Uttara Khanda of the Brahmanda Purana. The name of the chapter is " Shri Lalitaa Rahasya naama Saahasra Stotra Kathanam "
Iti Shri Brahmaanda Puraaney Uttara Khandey
Shri Hayagreevaagasthya Samvaadey
Shri Lalitaa Rahasya naama Saahasra Stotra Kathanam Naama Dwiteeyodhyaayah
Thus ends the 2nd chapter named " Sri Lalita Rahasya Nama Sahasra Stotra Kathanam" of the Uttara Khanda of the Brahmanada Purana which is in the form of a dialogue between Sri Hayagreeva & Sri Agastya.
The Lalita Sahasranama from the Brahmanda-Purana resembles the actual Lalita-Sahasranama which is often seen as an individual work, and is famously commentted upon by Bhaskararaya.
The final part of the Brahmanda Purana is also known as the Lalitopakhyana (Lalita Mahatmya) and constitutes chapters 5-44 of the final portion (Uttarabhaga) of the Brahmanda-Purana. The Lalita Sahasranama is based on the last four chapters (41, 42, 43 and 44) of this Lalitopakhyana and incudes a "thousand-syllabled" praise in chapter 43.
According to S. K. Ramachandra Rao:
The best-known work of his is on Lalita-sahasranama. This popular text has been constructed on the basis of Lalitopakhyana, which constitutes the last four chapters, 41 to 44 of Brahmanda-purana. This text recounting the thousand significant names of Lalita (also called Lalitamba, Parabhattarika, Lalita-tripura-sundari and Rajarajesvari) is in three chapters, altogether consisting of 320 verses.