Any way to check the clock speed of my processor?

From the command line type lscpu. The information will be at CPU MHz:

~$ lscpu | grep MHz
CPU MHz:               804.901
CPU max MHz:           3200.0000
CPU min MHz:           800.0000

There are a couple of ways:

1. lscpu or more precise lscpu | grep "MHz".
   This will give you the general MHz for the CPU.

   $ lscpu | grep "MHz".
   CPU MHz:               1600.000
   

2. cat /proc/cpuinfo or more precise cat /proc/cpuinfo | grep "MHz".
   This will give you the individual MHz for each CPU Core. So if you have an Core 2 Duo, AMD Bulldozer, Core i7, etc.. it will show the MHz for each core.

   $ cat /proc/cpuinfo | grep "MHz"
   cpu MHz     : 1600.000
   cpu MHz     : 1600.000
   cpu MHz     : 1600.000
   cpu MHz     : 1600.000
   cpu MHz     : 1600.000
   cpu MHz     : 1600.000
   cpu MHz     : 1600.000
   cpu MHz     : 3400.000
   

3. lshw -c cpu or more precise version: lshw -c cpu | grep capacity
   Will give you the general MHz. Same as lscpu.

   $ lshw -c cpu | grep capacity
   WARNING: you should run this program as super-user.
          capacity: 1600MHz
   WARNING: output may be incomplete or inaccurate, you should run this program as super-user.
   

4. sudo dmidecode -t processor or more precise: sudo dmidecode -t processor | grep "Speed" Will not only give you a MHz in use but also the Maximum you can push / overclock your CPU to.

   $ sudo dmidecode -t processor | grep Speed
   [sudo] password for cyrex: 
       Max Speed: 4000 MHz
       Current Speed: 2666 MHz
   

Out of all of this, lshw and dmidecode provide the best information out of your CPU.

You can also target the current MHz detected by the kernel by querying the log files:

cat /var/log/dmesg | grep "MHz processor" - For the current detected MHz speed

cat /var/log/kern.log | grep "MHz processor" - For the current and past detected MHz speeds. Will not work in some cases, that is why I posted the dmesg one first.

And that's all I can remember from the top of my head. I am fairly certain there are other ways, just don't remember right now. Of course, talking about terminal ways.

For the current CPU speed one can dynamically watch this change in real time using:

sudo watch -n 1  cat /sys/devices/system/cpu/cpu*/cpufreq/cpuinfo_cur_freq

To see the maximum CPU speed, use:

cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_max_freq 

indicator-cpufreq-selector is a nice little indicator tool which shows your current cpu frequency. You can even select the desired cpu frequency.

However last update for this tool was on 2015-10-19.

This works fine for real-time processor speeds

 watch "grep 'cpu MHz' /proc/cpuinfo"

While this is active, you can also spam the processor to see what maximum real-time speeds it can reach by openssl speed