I have a test command which runs test projects and writes the result to {ProjectFolder}/TestResults/UnitTests.trx
dotnet test --logger "trx;LogFileName=UnitTests.trx"
I do have the MSTest plugin installed which converts from trx to junit format 
I've also added a link to the test results using a post/always/step block as follows:
  post {
    always {
      step ([$class: 'MSTestPublisher', testResultsFile:"**/TestResults/UnitTests.trx", failOnError: true, keepLongStdio: true])
    }
  }
My declarative Jenkinsfile pipeline:
pipeline {
  agent any
  stages {
    stage('Restore') {
      steps {
        sh 'dotnet restore'
      }
    }
    stage('Test') {
      steps {
        sh 'dotnet test --logger "trx;LogFileName=UnitTests.trx"'
      }
    }
    stage('Build') {
      steps {
        sh 'dotnet build'
      }
    }
    stage('Stop') {
      steps {
        sh 'sudo systemctl stop core-app.service'
      }
    }
    stage('Deploy') {
      steps {
        sh 'rm -rf /var/www/core-app'
        sh 'cp -R . /var/www/core-app'
      }
    }
    stage('Start') {
      steps {
        sh 'sudo systemctl start core-app.service'
      }
    }
  }
  post {
    always {
      step ([$class: 'MSTestPublisher', testResultsFile:"**/TestResults/UnitTests.trx", failOnError: true, keepLongStdio: true])
    }
  }
  tools {
    msbuild '.NET Core 2.2.103'
  }
  environment {
    ASPNETCORE_ENVIRONMENT = 'Production'
  }
}