Find DOM element by ID when ID contains square brackets?

You need to escape the square brackets so that they are not counted as attribute selectors. Try this:

alert($("#something\\["+id+"\\]").parent().parent().attr("id"));

See Special Characters In Selectors, specifically the second paragraph:

To use any of the meta-characters (such as !"#$%&'()*+,./:;<=>?@[\]^``{|}~) as a literal part of a name, it must be escaped with with two backslashes: \\. For example, an element with id="foo.bar", can use the selector $("#foo\\.bar"). The W3C CSS specification contains the complete set of rules regarding valid CSS selectors. Also useful is the blog entry by Mathias Bynens on CSS character escape sequences for identifiers.