While using onetime encryption is it possible that one can deduce the key of a message if the contents of the message are already known? Let's say we have a randomly encrypted message and I pasted the contents of that message on a blog for some reason I do not share the key. 

Would you be able to figure out the key?

This is the message not encrypted:

This is the message.


This is the encrypted message:

 -----BEGIN OneTime MESSAGE-----

Version: OneTime 1.122

Pad ID: b1255b5389588da3c0e00b87213afb6bd79a0bbb

Offset: 0

QlpoOTFBWSZTWUyTjxYAAAJ+gAgCA4FKYABwSAEoAQAQIAAigA0xMEKBpoZGTEHGQdDBjUXXyo7R
HxdyRThQkEyTjxY=

-----END OneTime MESSAGE-----


The package will not let you use keys twice. Its protocol follows this rule especially for communicating to two computers over telnet, nc, ssh, etc. The protocol can be found here in this link https://www.red-bean.com/onetime/ .
Knowing the plaintext and ciphertext will allow you to recover (a portion of) the key.  

The OneTime package referenced in the comments implements a simple one-time pad.  Because the plaintext and ciphertext are related by a simple XOR it is trivial to calculate the portion of the one-time pad that is used for that message.  If all of the rules for using a one-time pad are followed (e.g. no re-use, truly independent random values for each bit, etc), then that portion of the key can be calculated, but it wouldn't provide any value beyond what was already known.