i'm not sure how. as i understand it, schnorr signatures simply incentivize coinjoin-type transactions (they'll become cheaper).

anyway, wire tapping implies they're already analyzing your internet traffic and probably hitting up your ISP and third party services for your logs. coinjoin adds some obfuscation, but some transactions can be revealing on their face due to input/output amounts. and it has problems that would be magnified by said traffic analysis. for example, they are prone to sybil attacks: if they know where you participate in coinjoins, they can act as the other participants to decipher your transactions. plus, the server-based coinjoin model is problematic because it entrusts whoever runs the server with your data (like electrum servers)---more honeypot fears. and IMO it probably won't save you if they're already linking your wallet outputs to you with a high probability (see here). and if you're tapped, you better be encrypting outgoing traffic---but then you better hope your VPN isn't a government honeypot. yes i'm paranoid!

if you think you're getting tapped, you should be thinking bigger than schnorr signatures......