You can use this as a starting point:
CREATE TABLE #DBTables (Name NVARCHAR(256), ID INT IDENTITY)
INSERT #DBTables
SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_TYPE='BASE TABLE'
DECLARE @Count INT, @RC INT
SET @RC = @@ROWCOUNT
SET @Count = 1
WHILE (@Count < @RC)
BEGIN
DECLARE @TableName NVARCHAR(256)
SELECT @TableName = Name FROM #DBTables WHERE ID = @Count
DECLARE @Query NVARCHAR(MAX)
SET @Query = 'SELECT * FROM ' + @TableName + ' WHERE Day = ''Monday'' AND Period4 = NULL'
EXEC(@Query)
SET @Count = @Count + 1
END
DROP TABLE #DBTables