Final answer:
To count the number of non-null observations per column, examine each column in a table or dataset and tally the number of non-null values present.
Step-by-step explanation:
In order to count the number of non-null observations per column, you will need to examine each column in a table or dataset and tally the number of non-null values present. You can do this by going through each row in the column and keeping track of the non-null values encountered. For example, if you have a column with 100 cells and 10 of them are null, then the number of non-null observations for that column would be 90.