The only way I can think of is to find parent ‘tr’ and then to get ‘td’ data at needed position. For example if company_id is third column you could do:
var company_id = $(this).parents('tr').find('td').eq(3).text();
or something like that.
Anyway this looks ugly and the only good solution here would be to somehow have the entire data row in associative array. Of course this should be handled by the framework.
Although I like GridView implementation I disagree with one design decision: not to have data in client objects. It would be much more intuitive to have client object that holds row collection then having to traverse dom every time you need key for specific row (for example), or when you need data from cell.