Along with the Logs you've already identified, the following can be used with Tableau directly to try and interpret what is causing slow performance:
That being said, if you Google "Tableau Slow Performance" you will find a variety of links that offer suggestions and helpful information on how to improve performance inside of Tableau.
What database are you using.
As Matt mentioned, performance recording is a good place to start.
If you have 1-3 queries that are taking most of those 2 minutes then you can turn to your DBA to see if you can tweak database (indexing, partitioning, keys etc) and/or dissect those queries to identify weak spots (complex string manipulations, subqueries etc).
Once you have that you can turn to dashboard tweaks in order to help Tableau generating slimmer queries (extra filters, joining tables vs Custom SQL etc.)
Performance optimization is an art.
I am connected to Amazon Redshift. I am fairly new to DB tweaking in terms of Indexing, portioning, etc. Can you direct me to some resources with regards to references.
Second, I have already analyzed the results of Tableau Performance monitor tool, It shows Queries are taking longer to execute. Is there any way I can see what queries does Tableau build to hit the Database? Can I use the same queries to query the Database ?