Raspberry multiple accelerometers please help with schematic
The SDO pin is used for I2C addressing. There are no internal pullup or pulldown resistors and therefore they must be connected to a valid level.

Connect one of them to ground and the other to Vdd(io); that way you get two devices on the I2C bus at different addresses (see below). I would normally connect these through a resistor (4.7k to 47k is a common range to use).

CS must likewise be connected.

The datasheet has this to say (page 19)


  With the ALT ADDRESS pin high, the 7-bit I2C address for the device is
  0x1D, followed by the R/W bit. This translates to 0x3A for a write and
  0x3B for a read. 
  
  An alternate I2C address of 0x53 (followed by the R/W bit) can be
  chosen by grounding the ALT ADDRESS pin (Pin 12). This translates to
  0xA6 for a write and 0xA7 for a read. 
  
  There are no internal pull-up or pull-down resistors for any unused
  pins; therefore, there is no known state or default state for the CS
  or ALT ADDRESS pin if left floating or unconnected. 
  
  It is required that the CS pin be connected to VDD I/O and that the
  ALT ADDRESS pin be connected to either VDD I/O or GND when using I2C.


I2C always requires a pullup on the SDA line (it is open drain), but the 4.7 ohm device you have on the schematic is not going to be close; try 2.2k as a start.

Whether you need a pullup on SCL depends on the output of the controller (but it won't hurt for one to be there); once more, you have a part identified that is simply nbot suitable - a 2.2k device would be a good starting point here as well.

Whether you need the 6.8 ohm device (R1) is debatable.

I will note that most people get asked if they have read the datasheet; as you are up-front about being new to this I am not going to make anything of it, but reading datasheets is a pre-requisite skill for virtually any task in electronics, so I would urge you to read through the datasheet and ask us where you have doubts as to the meaning of certain areas.

Updated in response to comment:

The CS pin is required to be pulled high for I2C operation (see the datasheet excerpt); if it is not there you can have intermittent operation (if it is a CMOS input you could conceivably destroy the device).

I also noticed you are powering from 5V; the maximum operating voltage for the ADXL345 is 3.6V; a linear 3.3V regulator to power the device would be prudent. Pulll the SDA line to thast voltage (not 5V). SCL would need a bit of thought as well.