I would like to ask how can I change the width of a column of a max diff question
It does not look like you have an easy way to adjust this using the Question Layout tab, so you will have to do it using css under the styling tab. It looks like if you want to adjust all your columns in the Max Diff question you can add a width attribute to the .sg-type-table .sg-table styles. However if you want to just adjust say the Attribute text you will have to do it by adding the style tag manually in the text of the attribute. When I inspect the page the header for the Attribute column does not have a tag reference that you can access without adding manually.
I hope this helps.