Hi Ziad
This works assuming you have not used periods in your documents names other than those that have a file extension on them.
Make a Query in laserfiche to find all documents in your required Location for *.* (this basically will find all files that have a period in them)

Copy the Syntax and past it into your Search Query in LF Workflow, and change the NAME="*.*" to NAME<>*.* such as below.
{LF:Name<>"*.*", Type="D"} & {LF:LOOKIN="laserrepository\TestFolder"}
This should then identify in a query any document name that does not have a period in the name which is those files that do not have an extension (as all files with an extension would have a period in them)