how to display two digits after decimal point in a calculated column in SQL?

You could use TRUNCATE

TRUNCATE(X,D)

Returns the number X, truncated to D decimal places. If D is 0, the result has no decimal point or fractional part. D can be negative to cause D digits left of the decimal point of the value X to become zero.

Something like this:

select *, 
        TRUNCATE((TotalDeaths/TotalCases)*100,2) as PercentDeath, 
        TRUNCATE((TotalDeaths/population)*100,2) as DeathPercentPopulation
from ( select location, 
              population, 
              sum(newcases) as TotalCases, 
              sum(newdeaths) as TotalDeaths
      from deaths
      where continent is not null
      group by location
     ) as newtable
order by DeathPercentPopulation desc

Or you could use ROUND function.

The ROUND() function in MySQL is used to round a number to a specified number of decimal places. If no specified number of decimal places is provided for round off, it rounds off the number to the nearest integer.

Syntax :

ROUND(X, D) Parameter : This method accepts two parameters in the syntax, as mentioned above and described below –

X : The number which to be rounded. D : Number of decimal places up to which the given number is to be rounded. It is optional. If not given it round off the number to the closest integer. If it is negative, then the number is rounded to the left side of the decimal point.

select *, 
        ROUND((TotalDeaths/TotalCases)*100,2) as PercentDeath, 
        ROUND((TotalDeaths/population)*100,2) as DeathPercentPopulation
from ( select location, 
              population, 
              sum(newcases) as TotalCases, 
              sum(newdeaths) as TotalDeaths
      from deaths
      where continent is not null
      group by location
     ) as newtable
order by DeathPercentPopulation desc

Use the FORMAT() function instead of ROUND or TRUNCATE. It is designed for this. It also puts in 'thousands separators' based on the Locale.

You can use the ROUND() function : https://docs.microsoft.com/fr-fr/sql/t-sql/functions/round-transact-sql?view=sql-server-ver15

Use case :

select *, 
        (ROUND(TotalDeaths/TotalCases)*100, 2) as PercentDeath), 
        (ROUND(TotalDeaths/population)*100, 2) as DeathPercentPopulation)
FROM ...