For example I have a WS-C2960X-24PD-L, which has two SFP/SFP+ uplink port. If I bought one 10G and one 1G SFP transceiver module, can I use them on the same switch, or these two ports can works on the same speed at the same time?
(Its not an etherchannel, port 25 connects to sw A, port 26 connects to sw B, which hasn't 10G capability.)
No sure if you can have a mix of 1 and 10Gig at the same time.
From the installation guide
SFP and SFP+ Module Slots
The switch has either two or four 1-Gigabit SFP or two 10-Gigabit SFP+ module slots. The slots marked SFP+ support both SFP and SFP+ modules. The SFP slots support only the SFP modules.
4 1Gig or 2 10Gig if I am reading it correctly.
If you have not purchased the 2960x yet, look at the 3650 series. A bit more expensive but much better switches with more options. You can have a mix of 1 and 10Gig ports.
I had to replace 30 2960x switches with 3650s, because we had so many issues with them. I stay away from 2960x series.