What is the syntax to use siblings() and closest() in geb scripts?

[Saranya Garimella]

I have a table with a lot of columns. The column names are unique and every column has the same icon in it. 

Lets say the column names are A,b,c,d and e. All these columns have a icon in them. I want to click the icon thats in the C column. How do I click it?

I also posted this on stack overflow: 

https://stackoverflow.com/questions/59637147/how-to-use-siblings-and-closest-in-geb-test

Any suggestions are appreciated. Thank you!