Does the value of one cell exist in another column from a different spreadsheet?

Here in this first sample sheet, I want to know whether the value from one cell (i.e. E3) exists within a column (K:K) within another google sheet. (And then I want to know the same for the entire column)

You'll see where I've approximated a formula that explains what I want in T3, but I don't know what I really need it to say. I have the html code from the other sheet there, like you'd do in an import range, with the tab and range, but can you help form the formula, or am I just totally on the wrong track?

(this is the second sheet that it's looking in)