Where can I find some of the functionality, namely the symbols, from the LaTeX package AMSSymb in ConTeXt? For example, how do I place a
\blacksquare? Is there an equivalent in ConTeXt? I didn't find what I am looking for at contextgarden.
\blacksquare works in ConTeXt out of the box. To see a list of all supported symbols, you can use (in MkIV)
\usemodule[mat-11] \usemodule[cambria] \starttext \showmathfontcharacters \stoptext
which gives a listing of all Unicode characters in a font, and the corresponding ConTeXt name for the character (look for mathname).