I'm not sure if this is what you're trying to achieve, however If you have a SOAP Test step called Test Request and you want to use the value of the <soapenv:Header><web:token></soapenv:Header> of this request in another SOAP Test step you can refer this value in the second SOAP Test step request using the follow syntax:
<soapenv:Enveloppe ...
<soapenv:Header>
<web:token>${Test Request#Request#//soapenv:Header/web:token}</web:token>
The syntax ${Test Request#Request#//soapenv:Header/web:token} has three parts, the name of the test step, followed by the property (could be #Request or #Response), and finally the xpath to get the value //soapenv:Header/web:token.
UPDATED:
As you said you've two SOAP Test Request, the first one is called test an has the follow response:
<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
<soap:Body>
<ns1:authentification xmlns:ns1="http://ws.demowebservices.com/">
<bloc1>
<bloc2>
<idSession>e1c64cd9-b933-4f56-ae1f-0f7d7f23942b</idSession>
</bloc2>
</bloc1>
</ns1:authentification>
</soap:Body>
</soap:Envelope>
The second is named for example test 2 (don't care because the second name not affect your purpose) and has the follow request:
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/">
<soapenv:Header>
<web:token>${test#Response#//ns1:authentification/bloc1/bloc2/idSession}</web:token>
</soapenv:Header>
<soapenv:Body>
...
</soapenv:Body>
</soapenv:Envelope>
With ${test#Response#//ns1:authentification/bloc1/bloc2/idSession} you're referencing the idSession value of the test response correctly. Take a look on the http log tab when you send your test 2 as shown in the follow image:

Hope this helps,
<web:token>from anotherSOAPrequest or reponse? - albciff