Create a saved search that will show Invoices that are flagged as taxable where a tax item has been applied but have zero tax amount.

The information with respect to the taxable box being checked true/false cannot be set in the criteria nor be extracted in the saved search results.  You cannot also  extract details with respect to the tax box being checked at the line item level.  As alternate solution:

1.     Navigate to Lists > Search > Saved Searches > New > Transaction

2.     On Criteria tab > Standard subtab:

Type = is Invoice.

Tax Item = is none of - Not Taxable - and none (This will ensure a tax item is applied on the invoice).

Formula (Numeric); Formula= {taxamount} equal to 0.

3.     Optional Date range may be added to limit results.

The line items you see in the search results should be those that have the tax  box checked on the invoice. However, there is no other way to limit your criteria to only those items that have this line item tax box checked as  true.