Can I use a current transformer to measure voltage and current?
A CT clamp will measure current taken by the load from the supply it is being fed. So, if the supply voltage is 240 VAC and the load is 240 ohms then the CT will produce a signal indicative of 1 amp RMS flowing. 

If the supply were 200 VAC and the load were 200 ohms, the CT would also indicate 1 amp RMS flowing.

In other words, no, the CT doesn't have any facility to indicate what the supply voltage is nor what the load is. You cannot measure power or energy without both a current and voltage measurement device.