Backup and Restore of master KEY and Certificate are not working on same server but different DBs. I have SQL Server 2012 I am following these steps but still not able to DECRYPT the data at destination. 

In Source DB I have created Following: 

CREATE MASTER KEY ENCRYPTION BY   
PASSWORD = 'Analytics@2020';  

CREATE CERTIFICATE Certificate_Customer_Data  
   WITH SUBJECT = 'Customer Sensitive Data'; 

CREATE SYMMETRIC KEY EmailID_Key_01  
    WITH ALGORITHM = AES_256  
    ENCRYPTION BY CERTIFICATE Certificate_Customer_Data; 


Then I backup Master Key and Certificate from Source DB to files:

BACKUP MASTER KEY 
  TO FILE = 'C:\Shivendoo\MasterKey.bak'
  ENCRYPTION BY PASSWORD = 'Analytics@2020';


BACKUP CERTIFICATE Certificate_Customer_Data TO FILE = 'C:\Shivendoo\DBCertificate.cer'  
    WITH PRIVATE KEY (ENCRYPTION BY PASSWORD = 'Analytics@2020',  FILE = 'C:\Shivendoo\PrivateKey.pvk'); 


Next I restore Back to Destination DB 

RESTORE MASTER KEY 
  FROM FILE = 'C:\Shivendoo\MasterKey.bak'
  DECRYPTION BY PASSWORD = 'Analytics@2020'
  ENCRYPTION BY PASSWORD = 'Analytics@2020';

OPEN MASTER KEY DECRYPTION BY PASSWORD = 'Analytics@2020';

ALTER MASTER KEY ADD ENCRYPTION BY SERVICE MASTER KEY;

CLOSE MASTER KEY;


CREATE CERTIFICATE Certificate_Customer_Data FROM FILE = 'C:\Shivendoo\DBCertificate.cer'
  WITH PRIVATE KEY(FILE='C:\Shivendoo\PrivateKey.pvk',
                   DECRYPTION BY PASSWORD='Analytics@2020')



CREATE SYMMETRIC KEY EmailID_Key_01  
    WITH ALGORITHM = AES_256  
    ENCRYPTION BY CERTIFICATE Certificate_Customer_Data;


Finally I loaded data from Source using this query:

OPEN SYMMETRIC KEY EmailID_Key_01  
   DECRYPTION BY CERTIFICATE Certificate_Customer_Data

SELECT ENCRYPTBYKEY(KEY_GUID('EmailID_Key_01'), [EMAIL]) AS [EMAIL]
FROM [dbo].[Source_Table]


Data loaded with encryption to Destination but when I try to Decrypt at destination using below query, It returns as NULL value for column DecryptedEmail 

OPEN SYMMETRIC KEY EmailID_Key_01  
   DECRYPTION BY CERTIFICATE Certificate_Customer_Data

SELECT CONVERT(NVARCHAR, DECRYPTBYKEY([EMAIL])) AS DecryptedEmail,[EMAIL],* FROM [dbo].[Destination_Table]


Please can you help..?

I am not getting any error but not getting expected outcome at Destination DB when I try to Decrypt Email at Destination which was Encrypted at Source.
The problem here is that your symmetric keys are not the same key, so it cannot be used in the destination database to decrypt the database on another database/instance/machine. Take a look at this link which describes the encryption hierarchy in SQL Server.

Basically, what is happening is you're creating a symmetric key on Source and using that to encrypt the column data. That symmetric key is protected (encrypted) by the certificate, the certificate is protected (encrypted) by the database master key and the DMK is protected (encrypted) by the service master key.

When you restore the DMK and Certificate to the destination database and create the new symmetric key, this doesn't allow you to decrypt the original data because the encryption was done by a different symmetric key.

In order to decrypt the data, you need to create an identical symmetric key. You achieve this by specifying the KEY_SOURCE and IDENTITY_VALUE properties of the symmetric key at creation time. By default, these values are randomly generated unless you specify explicit values.

By providing explicit values, an identical key is created and can be used on a different database/instance/machine to decrypt data encrypted by the source symmetric key. You can even use different certificates and database master keys to protect your destination symmetric key, it won't affect the decryption because the symmetric key is identical to the source key and once opened will decrypt the data.