DSLAMs are usually placed as close as practical to the CPE -- because it's distance constrained. So they can be in someone's yard, hanging on a pole, buried in a vault (CEV), or in a nearby CO. The upstream connection to the DSLAM could be going almost anywhere -- T-carrier and OC lines aren't so distance sensitive. In my experience, ATM (and frame) switches, and multiplexers, are in COs (or remote offices.) They are interconnected in a loop ("ring"), and/or mesh. The broadband aggregation router(s) (BRAS) can be anywhere (CO, RO, DC, closet in a shopping mall...); they just need power, and links to the ATM network and IP network.
(Ours were in major COs, as were the four (4) ATM switches. Frame-relay switches were in every CO.)
Note: as these are layer-2 technologies, they cannot be detected by
traceroute. The only way to know about them is for the operator(s) to tell you about them. As you have zero control over them, you rarely need to know about them. [You're paying someone to connect point A to point B; how they do it isn't your problem.]