I'm trying to mine on ropsten testnet. My hashrate is 108905. I think this is very low. Are there any ways to see required hash rate to mine?
You could use a mining calculator to estimate the average amount of time it would take you time successfully mine at that hashrate.
That page is set up for calculations on the main network, so you would first need to work out the combined network hashrate on Ropsten. This page shows that it's currently ~0.023 GH/s.
Leaving the other values the same (you might want to tweak them for your specific case - and the actual value of test ether is supposedly $0), and with your hashrate of 108905 H/s (i.e. 0.108905 MH/s)...
It will take you an average of 0.05 day to find 1 Block