How do I freeze panes in Numbers?

Have you tried Header Rows and Header Columns in Numbers? If you have Header Rows and/or Header Columns you can choose Freeze Header Rows and Freeze Header Columns from the Table menu.

Keep in mind that Numbers is designed for you to work with relative small tables, with multiple tables to a sheet if you want, rather than with a single big expanse of cells as in Excel. Because of that big expanse of cells in Excel, you more often need to be able to freeze. There is less of a need for that in Numbers.

SG

you can access the online manual that has a topic called "Add, remove, or freeze header rows and columns"

the topic is under the Create and Modify tables topic

Here: Online numbers Guide

Jason