Count rows in a table based on a DATE field
You have to utilise the COUNT function along with the GROUP BY function along the lines of

SELECT
 date_added AS Date,
 COUNT(Client_ID ) AS no_of_rows 
FROM CLIENTS
GROUP BY date_added  
ORDER BY date_added; 


Using the above produces output in the form of 

Date        no_of_rows
2019-03-01  1
2019-03-02  2
2019-03-03  3
2019-03-06  2


As an aside it is generally a good idea not to name a column with the name of a datatype i.e I would probably call the Data column in the result ClientDate.