Diodes facing each other in a circuit
If you are not told something about the diodes, then it's not possible to give a numeric answer, only a descriptive one. For large input voltages, the output current is approximately plus or minus \$I_S\$, depending on input polarity, so the output voltage will be approximately +/-\$1000I_S\$ volts. For small input voltages the output drops and passes through zero when the input does

If you are told the value for their saturation current \$I_S\$ and their ideality factor n (a frig factor often left at 1 for an ideal diode, but can be up to 2, or higher in some cases, to match observed behaviour), then you can use the Shockley equation, where the thermal voltage (26mV at room temperature) is \$V_T=\frac{kT}{q}\$, k is Boltzman constant, q is charge on one electron, T absolute temperature, \$V_D\$ the voltage across the diode

$$I=I_S(e^{\frac{V_D}{nV_T}}-1)$$

For large input voltages, this will still give you the descriptive result above, but it will allow you to fill in the detail of how the output voltage passes through zero.