I am linking data in one Master worksheet to another Slave worksheet in the same workbook.
Are you sure you are using LibreOffice? Calc calls these "sheets" and "spreadsheets"; you are using the language of Another Product!
The Master worksheet has blanks in its data. These blanks will be filled in at some future time - hence I need to be able to link those blank cells to the Slave worksheet. Libre Office Help says Copy the data, open the Paste Special dialog, tick the "paste all" box, and the "Link" box, and click OK. Doesn't work for me. What am I doing wrong?
Nothing, it seems: apparently empty cells are not linked. (You must mean that your cells are empty, not that they "have blanks".)
There is an easy workaround. Just fill your empty cells in the source with some placeholder and then paste the link to the new range with noi empty cells. You could leave the placeholders until the source cells needed their real values or you could remove the values after you have created the links.
You say that your source range "has blanks in its data", by which I believe you must mean empty cells. If your cells contain blanks - a string of one or more blanks - you will not see the problem. A blank string, then, is a perfectly suitable placeholder.
Note that if you empty the source cells after creating the links, you may find that the target cells will show as zero, not empty. If necessary, you can work around this is various ways, including perhaps setting the cell format to #.
I trust this helps.
Brian Barker