One source is the balance sheet . It is a snapshot of how the company stands at a single point in time. On the left are assets - everything the company owns. Things that can quickly be turned into cash are current assets . On the right are liabilities - everything the company owes.
Current liabilities are the debts due in one year, which are paid out of current assets.
If working capital shrinks, it could mean trouble. Look for growth in the stockholder's equity . It is the difference between total assets and liabilities. It is the presumed dollar value of what stockholders own. You want to see that it grows.